14 A survey was conducted into the health of 120 teachers.
The survey recorded whether or not they had suffered from a range of four health issues in the past year.
In addition, their physical exercise level was categorised as low, medium or high.
50 teachers had a low exercise level, 40 teachers had a medium exercise level and 30 teachers had a high exercise level.
The results of the survey are shown in the table below.
| Low exercise | Medium exercise | High exercise |
| Back trouble | 14 | 7 | 10 |
| Stress | 38 | 14 | 5 |
| Depression | 9 | 2 | 1 |
| Headache/Migraine | 4 | 5 | 5 |
14
- Find the probability that a randomly selected teacher:
14 - suffers from back trouble and has a high exercise level;
14
- (ii) suffers from depression.
14 - (iii) suffers from stress, given that they have a low exercise level.
14 - For teachers in the survey with a low exercise level, explain why the events 'suffers from back trouble' and 'suffers from stress' are not mutually exclusive.