Compare mean and median with five reading sessions
The mean adds all the values and divides by their number; the median identifies the middle value after the values are put in order. Both can summarize a set of reading-session lengths, but they answer slightly different questions. Use a small invented set to see why one unusually long session can change the mean more than the median. This is a calculation exercise, not evidence about how long anyone should read or how reading time affects learning.
Write a clear data set
Imagine five sessions lasting 10, 15, 15, 20, and 40 minutes. Write each duration on a separate card or on its own line. Add the unit minutes to the heading. These are five observations, including two separate sessions of 15 minutes. Do not remove a repeated value as if it were a duplicate typing error. Two observations can legitimately have the same value, and both belong in the calculation when both sessions occurred.
Before calculating, predict a reasonable range for the mean. It must fall between the smallest and largest durations, so an answer of 80 minutes would clearly be wrong. This range check does not prove a result is correct, but it catches some mistakes cheaply. Also note that the data describe duration, not the number of pages read. A summary of minutes cannot tell you which session covered the most material without additional information.
Calculate the mean step by step
Add the durations: 10 plus 15 plus 15 plus 20 plus 40 equals 100 minutes. Count the observations: there are five sessions. Divide 100 by 5 to obtain a mean of 20 minutes per session. Keep the count and the total visible in your working. A common error is dividing by the number of different durations, which would be four here. The mean uses the number of observations, including repeated values.
Check by multiplying the mean by the count. Twenty times five returns 100, the original total. This is a useful arithmetic check. You can also imagine redistributing the total time equally across the five sessions: each would receive 20 minutes. That equal-share interpretation explains why the mean uses all the values. It does not mean that every actual session lasted 20 minutes; the summary is a calculated equal share of the total.
Find the median separately
Put the values in ascending order: 10, 15, 15, 20, 40. They are already ordered in this example, but write the ordered list anyway. With five values, the third is the middle one, so the median is 15 minutes. There are two observations on either side of that third position. The repeated 15 does not cause a problem. The median is determined by ordered position, not by choosing a value that looks visually central on the page.
For contrast, consider four sessions lasting 10, 15, 20, and 40 minutes. There are now two middle positions, containing 15 and 20. Their mean is 17.5, so the median for that four-value set is 17.5 minutes. It need not be one of the original observations. Keep this even-count example separate from the original five-session calculation. Mixing lists midway through a problem can produce a correct calculation for the wrong data set.
Change one value and compare
Return to the original five sessions and replace 40 with 90. The ordered values become 10, 15, 15, 20, 90. Their sum is 150, and their mean is 30 minutes. The median remains the third value, 15 minutes. The long session increased the total by 50 minutes, which adds 10 minutes to the mean across five observations. The middle ordered position did not change, so the median stayed the same.
This comparison shows why the summaries can differ without either calculation being wrong. If you want the equal-share duration represented by the total time, the mean is directly relevant. If you want the middle observed duration by position, the median gives that information. Avoid saying that one is always the true average while the other is misleading. State which measure you used and why it answers your particular question about the data.
Explain the limits of the example
Five invented sessions are enough to teach the calculations, but they do not establish a population pattern. Do not turn this exercise into a claim about students, age groups, or effective reading habits. A real record also needs a clear definition of a session. Does a break end one session and start another? Are partial minutes rounded? Consistent definitions matter because a precisely calculated summary can still summarize inconsistently recorded observations.
When reporting a real set, include the number of observations and the unit. Mean duration 20 minutes across five sessions is more informative than average 20. If the distribution matters, show the small list or a simple plot alongside the summary. The mean and median each compress information. Neither tells a reader the complete spread, the sequence of sessions, or the circumstances that produced them. Choose the amount of detail appropriate to the decision.
Try your own five-card exercise
Use the values 8, 12, 12, 18, and 25. Find the total, mean, and median before checking: the total is 75, the mean is 15, and the median is 12. Now replace 25 with 50 and predict which summary changes. Calculate again and explain the result in one sentence that names the measure and unit. Can you describe why the mean changes while the median remains fixed without using the vague phrase because averages are different?
