### Data Management Lessons

How to organize data using frequency table and stem and leaf plot

Example 1

The marks awarded for an assignment set for a Year 8 class of 20 students were as follows:
6     7     5     7     7     8     7     6     9     7
4     10   6     8     8     9     5     6     4     8

Present this information in a frequency table.

Solution:

To construct a frequency table, we proceed as follows:

Step 1:

Construct a table with three columns.  The first column shows what is being arranged in ascending order (i.e. the marks).  The lowest mark is 4.  So, start from 4 in the first column as shown below.

Count the number of tally marks for each mark and write it in third column.

#### Example 2

The number of calls from motorists per day for roadside service was recorded for the month of December 2003.  The results were as follows:

Set up a frequency table for this set of data values.

Solution

Step 1:  Construct a table with three columns, and then write the data groups or class intervals in the first column.  The size of each group is 40.  So, the groups will start at 0, 40, 80, 120, 160 and 200 to include all of the data.  Note that in fact we need 6 groups (1 more than we first thought).

Step 2:  Go through the list of data values.  For the first data value in the list, 28, place a tally mark against the group 0-39 in the second column.  For the second data value in the list, 122, place a tally mark against the group 120-159 in the second column.  For the third data value in the list, 217, place a tally mark against the group 200-239 in the second column.

We continue this process until all of the data values in the set are tallied.

Step 3:  Count the number of tally marks for each group and write it in the third column.

Do it yourself:

The data below depicts the amount of time (in minutes) 20 middle school students spent on the computer each day. Arrange the data on a frequency table.

10, 32, 8, 55, 5, 0, 30, 20, 25, 45, 40, 60, 45, 15, 5, 56, 47, 12, 15, 20

 Number of Minutes on the Computer Tally Frequency 0 – 5 I I I 3 6 – 10 I I 2 11 – 15 I I I 3 16 – 20 I I 2 21 – 25 I 1 26 – 30 I 1 31 – 35 I 1 36 – 40 I 1 41 – 45 I I 2 46 – 50 I 1 51 – 55 I 1 56 – 60 I I 2

STEM AND LEAF PLOT

EXAMPLE 1

Complete a stem-and-leaf plot for the following list of grades on a recent test:

73,  42,  67,  78,  99,  84,  91,  82,  86,  94

use the tens digits as the stem values and the ones digits as the leaves. For convenience sake, order the list, but this is not required:

42,  67,  73,  78,  82,  84,  86,  91,  94,  99

Since I know where these data points came from ("a recent test"), I'll use a title. Then my plot looks like this:

 Stem Leaf 4 5 6 7 8 9 273,82,4,61,4,9

Do it yourself now

Complete a stem-and-leaf plot for the following list of values:

100,  110,  120,  130,  130,  150,  160,  170,  170,  190,
210,  232,  243,  262,  275,  275,  289.  290,  290

Ċ
Ms J. Jafri RTMS,
Jan 28, 2016, 8:51 AM
Ċ
Ms J. Jafri RTMS,
Feb 4, 2016, 8:45 AM
Ċ
Ms J. Jafri RTMS,
Feb 4, 2016, 8:45 AM
Ċ
Ms J. Jafri RTMS,
Feb 4, 2016, 8:46 AM