A number is chosen at random from the natural numbers 1 to 50. What is the probability that it is a prime number?

The primes up to 50 are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43 and 47 — fifteen of them — so the probability is 15/50 = 3/10. Counting 1 as a prime gives 16/50 = 8/25, and dropping 2 because it is even gives 14/50 = 7/25; 2 is prime and 1 is not. The option 1/2 assumes primes are as common as non-primes, which fails long before 50.