1.9 Stem and leaf diagrams

A group of students challenged their teachers to a speed-texting competition. The 21 participants (12 students and 9 teachers) were each required to send a short text message on a mobile phone. Their times are given in Figure 3 in order of size.

Figure 3 Speed-texting scores

Show description|Hide description

Table showing student and teacher times (in seconds) for a speed texting competition in an ordered list. Student times: 19, 19, 21, 24, 24, 25, 29, 30, 30, 33, 41 Teacher times: 18, 27, 28, 31, 33, 33, 36, 47, 51.

Figure 3 Speed-texting scores

Creating a stem and leaf diagram involves finding the ‘stems’, in this case the tens, and then recording the ‘leaves’ in order.

The stem and leaf diagram for the student times is shown in Figure 4. You can see that 1|9 represents 19 and 4|1 represents 41. There are no values between 0 and 10 which is shown as there are no leaves next to the stem 0. The greatest value in this data set is 41, so there are no values next to the stem 5 either.

Figure 4 An ordered stem and leaf diagram

Show description|Hide description

An ordered “stem and leaf” diagram for the students’ times, with “stem” 0 to 5 on the left hand side (in a vertical list) then a vertical line, before the “leaves”. Leaf values: 9 and 9 next to stem 1, 1, 4, 4, 5, 7 and 9 next to stem 2, 0, 0, 3 next to stem 3, 1 next to stem 4. There are no “leaves” next to stem 0 or stem 5. There is also a key showing that 1 line 9 means 19.

Figure 4 An ordered stem and leaf diagram