Question

Suppose that a natural number from 1 through through 11 inclusive is selected at random. What is the probability that the number selected is even if you know that it is prime?

Answer 1

0% Nothing even is prime, because all even numbers can be divided by 2.

Answer 2

2 is the only prime even number. Since it is only 1 of the 11 possibilities, the probability = 1/11

Answer 3

If you know that the number will be prime, than you only count the prime numbers; because there are 6 prime numbers in 1-11 and only one of those is even, the answer is 1/6.