Stem-and-Leaf Plots

Mentor: I am going to show you how to make a stem-and-leaf plot. These plots are used by statisticians to organize the data that they have better. We draw a line that looks a bit like a "T". On the left of the line we put the stem, which is all except the last number of each data point. On the right of the line we put the leaf, or the last number of the data point.

Student 1: So if I had a data point that is 57, I would put 5 on the left and 7 on the right?

Mentor: That's right. Who can tell me how I would put 257 on this plot?

Student 2: You would put 25 on the left and 7 on the right?

Mentor: Very good. Now, since I already have 57 on the chart, who can guess where I would put 53?

Student 3: You don't need a 5 on the left, since it's already there from the 57, but you need a 3 on the right. Could you put the 3 next to the 7?

Mentor: Wonderful thinking! It can be helpful to organize the numbers in order of magnitude so that we can see which ones occur more than once. If we added another 53, a 54 and two more 57's, it would look like this:

Student 4: Oh, I see, that way you can read the plot more easily when there is a lot of data on it!

Mentor: Right. As you can see, this chart could help us organize a large amount of information. I can see at a glance which number(s) would be in the middle of the data set or which ones occur most, and I can easily obtain the sum of the data points in order to calculate the mean, or average.