Fun fact: because half of all numbers are divisible by 2, we know that less than half of all numbers are prime. We also know that 1/3 of the remaining 1/2 are not prime because they are divisible by 3, so 1/2 + 1/6 of numbers are not prime-which is 2/3. We also know that numbers divisible by 5 aren't prime! So of the remaining 1/3 potential prime numbers, 1/5 are not prime, meaning 1/3*1/5 = 1/15. 1/15+2/3 = 11/15...