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

The answer to your question is 25hope this !