9 A teacher is investigating how pupils travel to and from school each day. Pupils can either travel by bus, train, car, bicycle or walk.
The teacher decides to collect a sample of size 60 for the investigation.
- The teacher lives in a village 10 miles away from the school.
Explain how collecting a sample which just consists of pupils who live in the same village as the teacher might introduce bias.
The table below shows how many students there are in each year.
| Year 7 | Year 8 | Year 9 | Year 10 | Year 11 |
| 86 | 105 | 107 | 101 | 101 |
- The teacher decides to use the method of proportional stratified sampling.
Calculate the number of pupils in the sample who are in Year 9.
The teacher generates a sample of 10 pupils from the 86 in Year 7 by listing them in alphabetical order and selecting the first name on the list and every ninth name thereafter.
- Explain whether this method will generate a simple random sample of the pupils who travel in Year 7.