Write all the natural numbers from 1 to 15. What fraction of them are prime numbers?

Natural numbers from 1 to 15 are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 and 15 Prime numbers from 1 to 15 are 2, 3, 5, 7, 11, 13, i.e., 6 prime numbers.

∴ Fraction of prime numbers = 6/15