Question

What is the probability, that a number selected from 1, 2, 3, …, 25, is a prime number, when each of the numbers is equally likely to be selected.

Answer 1

S = { 1, 2, 3, ---- , 25} |S|= 25 

And E = { 2, 3, 5, 7, 11, 13, 17, 19, 23 } |E|= 9 

Hence P(E) = |E| / |S| = 9 / 25.