Three of the most common graphs on the GED. Each one shows data in a different way — and almost every GED question asks you to compute something from the picture, not just read it.
A "data display" is just a picture of a set of numbers. The GED test uses three displays that confuse students the most: dot plots, histograms, and box plots. Each one shows the same kind of information (a list of numbers) in a different way, and you have to read them differently.
The most important thing to know up front: GED questions almost always require a calculation. The graph gives you the data — you still have to compute something from it: a mean, a range, a combined count, a comparison. Do not just look at the graph and pick the biggest bar.
⭐ The big idea
The graph holds the data. You still have to do the math.
🟢 Dot Plots
A dot plot shows individual data values. Each dot stands for one piece of data. You stack dots above the number they represent, so a tall stack means lots of values at that number.
Dot Plot
Shows individual values · 1 dot = 1 data point
Read the dot plot above:
2 students scored 7 → two 7s in the data set
4 students scored 8 → four 8s
3 students scored 9 → three 9s
3 students scored 10 → three 10s
Total: 2 + 4 + 3 + 3 = 12 students. The list of values is: 7, 7, 8, 8, 8, 8, 9, 9, 9, 10, 10, 10.
What you can compute from a dot plot: mean, median, mode, range, total count. Just write out the list of numbers from the dots, then run the calculation you need.
🟠 Histograms
A histogram looks like a bar graph — but it's not. The bars on a histogram represent ranges of values, not single values. This is the single most common GED data-display mistake.
Histogram
Groups values into ranges · each bar = a range, not 1 value
This histogram says 18 people are between 20 and 29 years old. It does not say there are 18 people who are exactly 20 — the bar covers everyone from 20 through 29.
Total people at the event: 5 + 12 + 18 + 9 + 6 = 50. To get the total, you add the frequencies of every bar.
⚠️ Most common GED mistake: Reading a histogram bar as one value instead of a range. If a bar is labeled "20–29", everyone in that bar is somewhere between 20 and 29 — you cannot tell exactly which age they are. The histogram only tells you which range they fall into.
🟣 Box Plots
A box plot is a summary picture of a whole data set. Instead of showing every value (like a dot plot) or grouping into ranges (like a histogram), it shows you five landmarks: the minimum, the maximum, the median, and the two edges of the middle 50% of the data.
Box Plot (Box-and-Whisker Plot)
Summary picture · five landmarks of the data set
What the five landmarks tell you:
Min (55): the lowest score in the class.
Max (98): the highest score.
Median (78): the middle score — half the class scored below 78, half above.
The box (70 to 88): the middle 50% of the class scored in this range.
The whiskers: show how far the data spreads out from the box.
What box plots are good for: comparing two data sets at a glance. Put two box plots side by side, and you can immediately see which group has a higher median, which group spreads out wider, and which group's middle 50% sits higher.
🔢 Worked Examples
Example 1 — Compute the mean from a dot plot
The dot plot below shows the number of books read this month by 10 students. What is the mean number of books?
Step 1. List every value the dots represent.
1, 2, 2, 2, 3, 3, 3, 3, 4, 5
Step 2. Count how many values there are.
10 students
Step 3. Add all the values together.
1 + 2 + 2 + 2 + 3 + 3 + 3 + 3 + 4 + 5 = 28
Step 4. Divide the sum by the count to get the mean.
mean = 28 ÷ 10 = 2.8 books
Example 2 — Find the range from a dot plot
Using the same dot plot above, what is the range of the data?
Step 1. Find the smallest value — look at the leftmost dot.
minimum = 1
Step 2. Find the largest value — look at the rightmost dot.
maximum = 5
Step 3. Subtract: range = max − min.
range = 5 − 1 = 4 books
Example 3 — Combine two histogram ranges
The histogram below shows test scores in a class of 30 students. How many students scored 80 or higher?
Step 1. "80 or higher" means two bars: 80–89 and 90–99.
Step 2. Read the frequency of each bar.
80–89: 11 students · 90–99: 8 students
Step 3. Add the two frequencies together.
11 + 8 = 19 students
Example 4 — Estimate the total from a histogram
Using the same histogram (shown again below), what is the total number of students in the class? You should not need to read a separate total — compute it from the bars.
Step 1. Read every bar's frequency.
60–69: 3 · 70–79: 8 · 80–89: 11 · 90–99: 8
Step 2. Add all four bars together.
3 + 8 + 11 + 8 = 30 students
Every student in the class belongs to exactly one range, so summing every bar gives the total.
Example 5 — Compare two box plots
Two classrooms took the same test. Their score distributions are shown below. Which class has the higher median? Which class has the wider spread of scores?
Step 1. Find each class's median (the vertical line inside its box).
Class A median ≈ 75 · Class B median ≈ 85
Step 2. Higher median:
Class B (85 > 75).
Step 3. Find each class's spread by computing range = max − min.
Class A: 92 − 60 = 32 · Class B: 98 − 70 = 28
Step 4. Wider spread:
Class A (its whiskers reach further apart).
⚠️ Common Mistakes
These are the slip-ups GED writers know students make. Watching for them is worth several questions.
1. Treating a histogram like a bar graph
Bars on a histogram represent ranges, not single values. If a bar covers "20–29", every person in that bar is somewhere from 20 to 29 — you cannot say they are exactly 25.
2. Forgetting to compute
The graph almost never gives you the final answer. You have to add, average, subtract, or compare. If your "answer" came from glancing at the graph in five seconds, it's probably wrong.
3. Misreading the scale
On a histogram, the y-axis might go up in steps of 2, 5, or 10 — not always 1. Read the gridlines carefully. Same for the x-axis on a box plot.
4. Confusing the median with the maximum on a box plot
The median is the line inside the box, not the right edge of the whisker. The right whisker tip is the maximum.
5. Ignoring grouped intervals when computing from a histogram
If a question asks "how many people are 30 or older?", you have to add every bar from 30–39 upward — don't just read one bar.
6. Forgetting to organize the data from a dot plot
Before computing the median or mean from a dot plot, write out the list of values. A dot in a tall stack is one value, not one dot — six dots stacked at "8" means six 8s in the data.