Answer:
The standard error of the proportion is 0.112.
Step-by-step explanation:
The standard error of a proportion is given by the following formula:
In which p is the probability of a success and n is the length of the sample.
In this problem
A success is a student defining themselves regular dietary supplement users. Our of 3000 students, 1500 do. So .
We take a sample of 20 of them, so .
So