The headteacher of a school wants to investigate opinions of pupils about meals sold in the canteen. she asks the first 20 people in the dinner queue their opinions.
explain why this is not a satisfactory method of selecting a sample of pupils.
describe how the headteacher could select a random sample of 20 students.

That is not a satisfactory sample because the results could be biased or viewed in a different way because maybe all 20 student the teacher chose may have a certain opinion. A good way to select random students is to maybe get some papers with all the student names and mix them all up in a bowl and then pick some random papers. 

The people who are in the front of the queue are the people most likely to like the food