4 The following back-to-back stem-and-leaf diagram shows the cholesterol count for a group of 45 people who exercise daily and for another group of 63 who do not exercise. The figures in brackets show the number of people corresponding to each set of leaves.
| People who exercise | | People who do not exercise | |
| (9) | 987643221 | 3 | 1577 | (4) |
| (12) | 988876653322 | 4 | 234458 | (6) |
| (9) | 877765331 | 5 | 1222344567889 | (13) |
| (7) | 6666432 | 6 | 12333455577899 | (14) |
| (3) | 841 | 7 | 245566788 | (9) |
| (4) | 9552 | 8 | 133467999 | (9) |
| (1) | 4 | 9 | 14558 | (5) |
| (0) | | 10 | 336 | (3) |
Key: 2 | 8 | 1 represents a cholesterol count of 8.2 in the group who exercise and 8.1 in the group who do not exercise.
- Give one useful feature of a stem-and-leaf diagram.
- Find the median and the quartiles of the cholesterol count for the group who do not exercise.
You are given that the lower quartile, median and upper quartile of the cholesterol count for the group who exercise are 4.25, 5.3 and 6.6 respectively.
- On a single diagram on graph paper, draw two box-and-whisker plots to illustrate the data.