GED Scientific Practices
Scientific practices are the reasoning skills that run through every part of GED Science. These questions give you an experiment, a table, or a described graph and ask what it tests, what it shows, or what it cannot show.
Question 1 of 24
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A student wants to know which of three paper towel brands absorbs the most water. Each towel is dipped in a bowl of water for 10 seconds, and the amount of water it absorbs is measured. Which factor must be kept the same for a fair test?
Scientific practices study guide
Scientific practices are the thinking skills behind every GED Science question. You will read an experiment, a data table, or a description of a graph and decide what it tests, what it shows, and what it cannot show. These skills apply in life, physical, and earth science alike, so practicing them pays off across the whole test.
Questions, hypotheses, and predictions
Science starts with a question that can be answered by collecting evidence. “Does fertilizer help tomatoes grow?” is a scientific question. “Are tomatoes the best vegetable?” is not, because “best” is an opinion that cannot be measured.
A hypothesis is a possible answer that can be tested. It usually names a cause and an effect: “Tomato plants given fertilizer will grow taller than plants given none.” A prediction states what you expect to see if the hypothesis is true. On the test, the correct hypothesis matches the one thing the experiment changes and the one thing it measures. A statement that is true but not tested by the experiment, such as “plants need water,” is a common wrong answer.
Independent, dependent, and controlled variables
Every experiment has three kinds of variables. The independent variable is the one the experimenter changes on purpose. The dependent variable is the one that is measured to see whether it responds. Controlled variables are everything that is kept the same so they cannot affect the result.
A quick way to sort them is to fill in this sentence: “The experimenter changed ___ to see how it affected ___.” The first blank is the independent variable and the second is the dependent variable. If a choice names something the passage says was kept the same, such as the amount of water or the size of the container, it is a controlled variable.
Worked example
A cook tests how oven temperature affects baking time. Identical loaves of bread dough are baked at 325°F, 350°F, and 375°F, and the time until each loaf is done is recorded. Name the independent, dependent, and controlled variables.
- The cook changed the oven temperature on purpose, so oven temperature is the independent variable.
- The cook measured how long each loaf took, so baking time is the dependent variable.
- The loaves were identical, so dough recipe and loaf size are controlled variables.
Designing a fair test
A fair test changes only one variable at a time. If a student puts one plant in a sunny window with music and another in a dark closet without music, two things changed at once. Even if the first plant grows more, there is no way to know whether light or music caused it.
Many experiments use a control group, which does not receive the treatment. The control group gives a baseline for comparison. In medical studies, the control group often gets a placebo, a look-alike pill with no active ingredient. When neither patients nor doctors know who got the real drug, the study is called double-blind, and expectations cannot tilt the results.
- Change one variable; keep everything else the same.
- Include a control group for comparison.
- Use many subjects and repeat each trial.
Sample size and repeated trials
Results from a few subjects can be swayed by chance. If a supplement is tested on four people and three feel better, that could easily be luck. Testing hundreds of people gives a more reliable picture. On the test, a question about improving reliability is usually answered by a larger sample, more repeated trials, or adding a control group.
Repeated trials also reveal errors. If four trials give similar results and a fifth is far off because of a known mistake, such as a bumped cart or a spilled sample, it is reasonable to leave that trial out of the average and explain why.
Reading tables and described graphs
Before you answer, read the title, the column or axis labels, and the units. Then describe the trend in your own words: does the measured value rise, fall, level off, or rise and then fall? Many GED graphs are described in words, so picture the line as you read.
Watch for a pattern that changes partway through. A table may show plant height rising with fertilizer up to a point and then dropping. The correct conclusion describes the whole pattern, not just the first part.
Calculations from experimental data
Three calculations come up again and again. An average (mean) is the sum of the values divided by how many values there are. A rate is the change in a quantity divided by the time it took. A percent change is the change divided by the starting value, times 100.
Worked example
A seedling is 5 cm tall at the start of a study and 26 cm tall after 7 weeks. What was its average growth rate?
- Find the change in height: 26 − 5 = 21 cm.
- Divide by the time: 21 ÷ 7 = 3 cm per week.
- Check the trap answer: 26 ÷ 7 is about 3.7, which forgets the starting height.
Worked example
A filter lowers the amount of a chemical in water from 50 parts per billion to 20 parts per billion. What is the percent decrease?
- Find the change: 50 − 20 = 30.
- Divide by the starting value: 30 ÷ 50 = 0.6.
- Multiply by 100: the level dropped by 60 percent.
Drawing conclusions the data support
A supported conclusion stays inside the evidence. If a study included only adult men, it cannot prove anything about children. If data stop at 3 hours of study, they cannot promise what 4 hours will do. Answer choices that use words like “always,” “guarantees,” or “proves” often go too far.
Also separate correlation from cause. When two things rise together, such as ice cream sales and heat illness, a third factor like hot weather may drive both. An observation describes what was seen; an inference tries to explain it. Know which one a question is asking for.
Checklist before test day
Check that you can do each of these quickly.
- Tell a testable hypothesis from an opinion.
- Name the independent, dependent, and controlled variables in a described experiment.
- Spot an experiment that changes more than one variable at once.
- Explain why a larger sample and a control group make results more reliable.
- Compute an average, a rate, and a percent change from a table.
- Reject a conclusion that goes beyond the data or confuses correlation with cause.
Scientific Practices practice set 1: 24 questions with answers
Work each question on paper first, then open the answer to check your reasoning.
1.A student wants to know which of three paper towel brands absorbs the most water. Each towel is dipped in a bowl of water for 10 seconds, and the amount of water it absorbs is measured. Which factor must be kept the same for a fair test?
- A.The price of each towel roll
- B.The size of each towel sheet
- C.The amount of water absorbed
- D.The brand of each towel tested
Show answer
Answer: B. The size of each towel sheet
Sheet size affects how much water a towel can hold, so it must be held constant. The brand is the variable being tested, so it is supposed to change.
2.A poultry researcher feeds three groups of hens different amounts of calcium for two months and counts how many eggs with cracked shells each group lays. What is the dependent variable?
- A.The amount of calcium fed
- B.The number of cracked eggs
- C.The length of the study
- D.The breed of the hens used
Show answer
Answer: B. The number of cracked eggs
The dependent variable is what is measured in response to the change, here the count of cracked eggs. The calcium amount is what the researcher changes, so it is the independent variable.
3.An adult education center tracked study time before a weekly quiz. No study: average score 58 1 hour: average score 67 2 hours: average score 75 3 hours: average score 82 Which conclusion is best supported by the data?
- A.Studying 4 hours would guarantee a perfect score
- B.Learners who did not study were not trying at all
- C.Average scores were higher with more study time
- D.Study time had no clear effect on average scores
Show answer
Answer: C. Average scores were higher with more study time
Each extra hour of study matches a higher average score. The data stop at 3 hours, so they cannot support a guarantee about 4 hours.
4.A city health report notes that on days when ice cream sales are highest, emergency rooms also treat the most cases of heat illness. Which interpretation is most reasonable?
- A.Heat illness likely makes people go out and buy ice cream
- B.The two numbers are linked only by random chance each day
- C.Hot weather likely raises both ice cream sales and heat illness
- D.Eating ice cream likely causes people to develop heat illness
Show answer
Answer: C. Hot weather likely raises both ice cream sales and heat illness
A third factor, hot weather, can drive both numbers up at once, so a link does not prove one causes the other. Concluding that ice cream causes heat illness mistakes correlation for causation.
5.A water company tests a new filter. Before filtering, a sample contains 40 parts per billion (ppb) of lead. After filtering, it contains 10 ppb. By what percentage did the filter reduce the lead level?
- A.25%
- B.400%
- C.30%
- D.75%
Show answer
Answer: D. 75%
The drop is 40 − 10 = 30 ppb, and 30 ÷ 40 = 0.75, or 75%. The 25% choice is the share of lead that remains, not the share removed.
6.A student heats 1 liter of water on each stove setting and records how long it takes to boil. Low: 14 minutes Medium: 9 minutes High: 6 minutes How many minutes faster did the water boil on high than on low?
- A.5 minutes
- B.6 minutes
- C.14 minutes
- D.8 minutes
Show answer
Answer: D. 8 minutes
14 − 6 = 8 minutes. The 5 minute choice compares low and medium instead of low and high.
7.A research team publishes a report that lists every material, measurement and step of its experiment in detail. What is the main reason scientists include this information?
- A.So other scientists can repeat the experiment and check results
- B.So no other scientist is allowed to perform the same experiment
- C.So readers can see how much money the experiment had cost
- D.So the results never need to be tested again by anyone else
Show answer
Answer: A. So other scientists can repeat the experiment and check results
Detailed methods let other researchers repeat the work, and repeated results make a finding more trustworthy. Science works the opposite way from the last choice: results are expected to be tested again.
8.In a study of a new pain reliever, half the patients receive the drug and half receive an identical-looking sugar pill. Neither the patients nor the doctors know who received which pill until the study ends. What is the main purpose of this design?
- A.To keep expectations from affecting the reported results
- B.To let the doctors choose the best patients for the drug
- C.To make sure that every patient receives the real drug
- D.To lower the cost of making the new pain-relief drug
Show answer
Answer: A. To keep expectations from affecting the reported results
When no one knows who got the real drug, hopes and expectations cannot tilt the pain reports or the doctors’ judgments. Half the patients get a sugar pill, so not every patient receives the real drug.
9.A student measures how far a toy car rolls off a ramp in five trials. 2.1 m, 2.3 m, 2.2 m, 5.9 m, 2.4 m The student later learns the car was bumped by a sibling during the 5.9 m trial. Leaving out that trial, what is the average distance?
- A.2.2 m
- B.2.25 m
- C.2.98 m
- D.5.9 m
Show answer
Answer: B. 2.25 m
The four valid trials add to 2.1 + 2.3 + 2.2 + 2.4 = 9.0 m, and 9.0 ÷ 4 = 2.25 m. The 2.98 m choice averages all five trials, including the one with the known error.
10.A community garden club wants to run an experiment. Which of these statements is a hypothesis that can be tested with an experiment?
- A.Plants given salt water grow less than plants given tap water
- B.Gardening is a more enjoyable weekend hobby than home cooking
- C.Houseplants feel happier when their owners talk kindly to them
- D.Roses are the most beautiful flowers anyone can grow at home
Show answer
Answer: A. Plants given salt water grow less than plants given tap water
Plant growth under two kinds of water can be measured and compared, so that statement is testable. Beauty, happiness and enjoyment are opinions or feelings that cannot be measured objectively.
11.A line graph shows a city’s electricity use over one weekday. Use is lowest around 4 a.m., rises through the morning, peaks around 6 p.m., and then falls through the night. Which conclusion is best supported by the graph?
- A.Electricity use stayed the same through the day
- B.Electricity use was highest just before sunrise
- C.Electricity use was highest in the early evening
- D.Electricity use was highest around noon each day
Show answer
Answer: C. Electricity use was highest in the early evening
The peak is described at about 6 p.m., which is early evening. Use around 4 a.m. was the lowest point, so the before-sunrise answer reverses the graph.
12.A student tracks a snail moving along a straight ruler. 0 minutes: 0 cm 5 minutes: 15 cm 10 minutes: 30 cm 15 minutes: 45 cm If the snail keeps the same pace, how far will it have traveled at 25 minutes?
- A.65 cm
- B.60 cm
- C.90 cm
- D.75 cm
Show answer
Answer: D. 75 cm
The snail moves 15 cm every 5 minutes, or 3 cm per minute, so 25 × 3 = 75 cm. The 60 cm choice is the distance at 20 minutes.
13.A student tests whether music helps plants grow. Plant A is placed by a sunny window with music playing. Plant B is placed in a dark closet with no music. After two weeks, Plant A is much taller. What is the main problem with this experiment?
- A.The student should have measured the color of the plants
- B.Light and music both changed, so the cause of growth is unclear
- C.Plant A should have been the one placed in the dark closet
- D.Music played in the room cannot reach plants inside a closet
Show answer
Answer: B. Light and music both changed, so the cause of growth is unclear
A fair test changes only one variable, but here light and music both differed, so either could explain the result. Swapping the plants’ locations would still leave two variables changing together.
14.A seed packet states that 80% of its seeds are expected to sprout. A gardener plants 50 seeds from the packet. About how many seeds should sprout?
- A.40
- B.80
- C.45
- D.30
Show answer
Answer: A. 40
80% of 50 is 0.8 × 50 = 40 seeds. The 80 choice confuses the percentage with the number of seeds.
15.A study followed 2,000 adult men for five years and found that those who walked daily had lower average blood pressure than those who did not. Which conclusion goes beyond what this study can show?
- A.Daily walking lowers blood pressure in children
- B.The study included a large number of adult men
- C.Daily walking was linked to lower blood pressure in men
- D.Blood pressure was measured in the men studied
Show answer
Answer: A. Daily walking lowers blood pressure in children
The study included only adult men, so it says nothing about children. The other statements simply restate what the study did or found.
16.A greenhouse worker records plant height after one month at different fertilizer amounts. 0 g: 10 cm 5 g: 16 cm 10 g: 21 cm 15 g: 22 cm 20 g: 15 cm Which conclusion is best supported?
- A.Height rose steadily with every increase in fertilizer amount
- B.The amount of fertilizer had no clear effect on plant height
- C.Height rose with fertilizer up to about 15 g, then fell at 20 g
- D.Plants with no fertilizer grew taller than all of the others
Show answer
Answer: C. Height rose with fertilizer up to about 15 g, then fell at 20 g
Heights climb from 10 cm to 22 cm and then drop to 15 cm at 20 g, so more fertilizer helped only up to a point. The drop at 20 g rules out a steady rise.
17.While on a trail, a hiker writes in a notebook: “The leaves on the large oak tree are brown and curled at the edges.” This statement is best described as
- A.an observation, because it describes what is seen
- B.a hypothesis, because it predicts a future result
- C.an inference, because it explains why the tree is ill
- D.a conclusion, because it is based on an experiment
Show answer
Answer: A. an observation, because it describes what is seen
The note records only what the hiker saw, which makes it an observation. It offers no explanation for the brown leaves, so it is not an inference.
18.An environmental scientist claims that a new road salt is harming streams near highways. Which evidence would best support this claim?
- A.The salt company states that its product is safe for nearby streams
- B.Road crews spread more salt this winter than they did last winter
- C.Snowfall totals in the area were higher this year than in past years
- D.Streams by salted roads had fewer insects than similar unsalted ones
Show answer
Answer: D. Streams by salted roads had fewer insects than similar unsalted ones
Comparing salted and similar unsalted streams links the salt to a measurable harm. Knowing that more salt was used says nothing about whether the streams were affected.
19.A science poster shows the water cycle as a single drawing. Arrows labeled evaporation, condensation and precipitation connect an ocean, clouds and a mountain. What is the main advantage of using this model?
- A.It shows a large, slow process in one simple picture
- B.It shows the exact amount of water at every moment
- C.It proves that the water cycle never changes at all
- D.It removes the need to collect any real-world data at all
Show answer
Answer: A. It shows a large, slow process in one simple picture
A model simplifies a process too large and slow to watch directly, so the whole cycle fits in one view. A simple diagram does not give exact amounts of water, which is a limitation of this kind of model.
20.Scientists built a computer model that predicts smog levels in a city. For five years, its predictions matched air measurements closely. This year, new measurements are much higher than the model predicted. What should the scientists do next?
- A.Ignore the new data since the model worked before
- B.Stop measuring so the model stays accurate
- C.Change the new data to match the model’s output
- D.Revise the model so it fits the new evidence
Show answer
Answer: D. Revise the model so it fits the new evidence
Models are tools that must be updated when reliable new evidence disagrees with them. Past success does not justify ignoring new data, and changing data to fit a model would be dishonest.
21.A researcher wants to learn how much exercise adults in a city get each week. The researcher surveys 300 people as they leave a large gym. What is the main problem with this sample?
- A.The researcher should have chosen an even larger gym to visit
- B.Adults cannot give answers to questions about their exercise
- C.People leaving a gym likely exercise more than most adults
- D.The survey asked too few questions about the foods people eat
Show answer
Answer: C. People leaving a gym likely exercise more than most adults
People at a gym are not typical of all adults, so the results would overstate how much the city exercises. A larger gym would still give the same kind of biased sample.
22.A bar graph shows how many bird species visited a backyard feeder each season. Winter: 6 species Spring: 14 species Summer: 11 species Fall: 9 species Which season had the second-highest number of species?
- A.Spring
- B.Winter
- C.Fall
- D.Summer
Show answer
Answer: D. Summer
Spring has the most species at 14, and summer is next at 11. Spring is the highest, not the second highest, which makes it the most tempting wrong answer.
23.A table shows how many grams of a salt dissolve in 100 g of water at different temperatures. 20°C: 34 g 40°C: 40 g 60°C: 46 g 80°C: 51 g About how many grams would dissolve in 100 g of water at 50°C?
- A.40 g
- B.86 g
- C.43 g
- D.46 g
Show answer
Answer: C. 43 g
50°C is halfway between 40°C and 60°C, so the amount should be about halfway between 40 g and 46 g, or 43 g. The answer 86 g adds the two values without dividing by 2.
24.A student tests this hypothesis: “Plants watered with rainwater will grow taller than plants watered with tap water.” Each group has 15 plants kept in the same sunny window. Which result would show the hypothesis is NOT supported?
- A.Each group of plants was given the same amount of water
- B.Both groups grew to about the same average height
- C.The rainwater group grew taller than the tap water group
- D.Both groups of plants grew in the same sunny window
Show answer
Answer: B. Both groups grew to about the same average height
If both groups end up the same height, rainwater did not make the plants taller, so the hypothesis is not supported. The other choices are either a result that supports it or conditions that were controlled, not results.
More practice sets
Scientific Practices has 2 practice sets. None of these questions appear in the full practice tests.
- Set 1: 24 questions (this page)
- Set 2: 24 questions
Hypotheses and variables on the GED
A hypothesis is a testable statement about how one thing affects another. The independent variable is what the experimenter changes on purpose. The dependent variable is what gets measured in response. Everything else should stay the same, and those are the controlled variables.
When a question describes an experiment, name these three parts before you read the choices. Most wrong answers swap the independent and dependent variables or name something that was held constant.
Fair tests, controls, and sample size
A fair test changes only one variable at a time. If light and music both differ between two plants, the result cannot be pinned on either one. A control group gets no treatment, or a placebo, so the treated group has something to be compared against.
Small samples make results unreliable. Four volunteers or one plant per group can be swayed by chance, so the strongest designs use many subjects and repeat each trial.
Drawing conclusions and simple calculations
A supported conclusion stays inside the data. If a study included only adult men, it cannot prove anything about children. If two things rise together, a third factor may cause both, so a link alone does not prove cause.
Expect averages (add the values, divide by how many), rates (change divided by time), and percent change (change divided by the starting value). Read each number from the table carefully and check which values the question asks you to use.
Frequently asked questions
- Is scientific practices a separate section of the GED Science test?
- No. These skills are tested inside life, physical, and earth and space science questions, which is why they show up so often.
- Do I need to memorize formulas for science calculations?
- Rarely. Questions usually give the formula or need only an average, rate, or percent, and the on-screen calculator is available.