The mean is the total divided by how many values there are. The median is the middle value in order, or the mean of the two middle values. The mode is the most common value, and the range is highest minus lowest. A probability is favorable outcomes over total outcomes. Try each one in the lab below.
The short answer
The mean is the total divided by how many values there are. The median is the middle value in order, or the mean of the two middle values. The mode is the most common value, and the range is highest minus lowest. A probability is favorable outcomes over total outcomes. Try each one in the lab below.
What the lab does
Free and interactive, with original practice items. Practice mode gives feedback on each step; test style asks for every answer first, then shows the result and the worked steps. Goes with GEDPilot lesson GP-M07, Data, Statistics and Probability: Make a Defensible Conclusion.
Mean, median, mode and range
How outliers affect each measure
Finding a missing value for a target mean
Weighted averages
Simple probability and complements
Independent and dependent compound events
Expected counts and experimental versus theoretical probability
Key facts (checked 2026-10-26)
Defined on the GED formula sheet: Mean, median
Not on the sheet: learn these: Mode, range
Every probability falls in this range (0% to 100%): 0 to 1
Probability that an event does not happen: 1 − P
How do you find the mean, median, mode and range?
Example data: 4, 8, 6, 5, 3, 8. In order: 3, 4, 5, 6, 8, 8.
Mean: add the values and divide by how many there are. 34 ÷ 6 = 17/3, about 5.67.
Median: the middle value in order. With an even count, average the two middle values: (5 + 6) ÷ 2 = 5.5.
Mode: the value that appears most often: 8. If two values tie, both are modes. If every value appears equally often, there is no mode.
Range: highest minus lowest: 8 − 3 = 5.
Which measure does an outlier change most?
An outlier is a value far from the rest. It pulls the mean toward it and stretches the range, while the median usually moves only a little. That is why the median often describes a typical value better when the data has an outlier, such as home prices or wait times. Use the outlier switch in the lab to see it happen.
How do you find a missing value or a weighted average?
Missing value: multiply the target mean by the total number of values to get the total you need, then subtract the values you already have. Scores 82, 90, 76 and 88 with a target mean of 85 over five quizzes: 85 × 5 = 425, and 425 − 336 = 89.
Weighted average: multiply each value by its weight and add. If homework counts 20%, the midterm 30% and the final 50%, then 80, 70 and 90 give 0.2 × 80 + 0.3 × 70 + 0.5 × 90 = 82.
How do you find simple and compound probability?
Simple probability is favorable outcomes ÷ total outcomes. The probability that something does not happen is 1 minus the probability that it does. For one draw, "red or blue" adds the two probabilities, because one chip cannot be both.
For two draws, "and" multiplies. If you put the first chip back, the draws are independent and the bag is the same both times. If you keep it out, the draws are dependent: the second fraction has one fewer chip in the total. With 3 red and 5 blue chips, P(blue, then blue) without replacement is 5/8 × 4/7 = 5/14.
Expected count = probability × number of trials. A real experiment usually lands near that number, not exactly on it.
What data and probability is on the GED math test?
GED Testing Service's assessment guide lists calculating the mean, median, mode and range, finding a missing value from an average, finding an average from frequency counts, calculating a weighted average, and finding the probability of simple and compound events. The GED formula sheet defines the mean and the median; mode, range and the probability rules are not on it.
Science and Social Studies also use data. GED.com lists an on-screen calculator for both, and for Part 2 of the Math test.
Worked sample questions (original practice, not GED test items)
Five deliveries took 18, 21, 25, 24 and 38 minutes. Which measure would change the least if the 38-minute delivery were removed? Answer: B, The median. With all five, the mean is 126 ÷ 5 = 25.2, the median is 24 and the range is 38 − 18 = 20. Without 38, the mean is 88 ÷ 4 = 22, the median is (21 + 24) ÷ 2 = 22.5 and the range is 25 − 18 = 7. The median moves 1.5 minutes, the mean 3.2 and the range 13, so the median changes least.
A bag holds 3 red chips and 5 blue chips. Two chips are drawn, one after the other, without putting the first one back. What is the probability that both chips are blue? Answer: B, 5/14. First draw: 5 of 8 chips are blue, so 5/8. The blue chip stays out, so 4 of the 7 chips left are blue: 4/7. Multiply: 5/8 × 4/7 = 20/56 = 5/14. Choice A is the answer with replacement (5/8 × 5/8).
Ana’s first four quiz scores are 82, 90, 76 and 88. What score does she need on the fifth quiz for a mean of exactly 85? Answer: C, 89. A mean of 85 over 5 quizzes needs a total of 85 × 5 = 425. The first four add to 336. 425 − 336 = 89. Check: (336 + 89) ÷ 5 = 85.
What to do next
Work through both modes of the lab: Try the statistics tools, then the chip bag. Read the worked steps after each answer: studying worked examples tends to help math performance (Barbieri and others, 2023), as a start before you practise on your own. Finish with a test-style set.
Read lesson GP-M07 in the workspace: Data, Statistics and Probability: Make a Defensible Conclusion (included with the book or a plan; GP-M01 is the free sample).
Use the free math reference: An 8-page PDF with the mean, median and probability methods in one place.
Take the free GEDPilot diagnostic: 32 original questions across all four subjects show which skills need the most work. It is practice, not an official score.
Check readiness with the official practice test: Book the real Math test after a green GED Ready result (Likely to Pass, 145 to 200). Too Close to Call (134 to 144) means a little more practice first.
Are mean and median on the GED formula sheet? Yes. The GED formula sheet defines the mean as the total of the values divided by the number of values, and the median as the middle value, or the mean of the two middle values when the count is even. Mode, range and the probability rules are not on it.
How do you find the median of an even number of values? Put the values in order and find the two in the middle. Add them and divide by 2. For 3, 4, 5, 6, 8 and 8, the middle values are 5 and 6, so the median is 5.5.
What if two numbers tie, or nothing repeats? Is there a mode? If two values tie for most frequent, both are modes. If every value appears the same number of times, the data set has no mode.
Which measure does an outlier change the most? The mean and the range. One very large or very small value pulls the mean toward it and stretches the range. The median usually moves only a little.
What is the difference between independent and dependent events? Independent events do not affect each other, such as drawing a chip and putting it back before the next draw. Dependent events do: if the first chip stays out, the second draw has one fewer chip, so the second fraction changes.
Can I give a probability as a fraction, decimal or percent? In this lab, yes. A repeating decimal counts when it is rounded to at least the hundredth, such as 0.33 for 1/3. On the real test, read each question for the form it asks for.
What GED math skills does this lab cover? Most of the data skills in GED Testing Service's assessment guide: mean, median, mode and range, a missing value from an average, a weighted average, and the probability of simple and compound events. Counting combinations and permutations is also on the list, and the lab does not cover it, so practise it in lesson GP-M07.
Independent preparation materials. Not affiliated with or endorsed by ACE or GED Testing Service. GED is a registered trademark owned by ACE. Practice results do not predict an official GED score, and GEDPilot does not guarantee a passing score.