Question

If i pick a number anywhere from 1 to 1000 at random, what is the probability that the number is divisible by either 2 or 5?

Answer 1

think of it kind of like a Venn diagram.

P(divisible by 2 or 5) = P(by 2)+P(by 5) - P(by 10)

So just count the number of integers divisible by 2 or 5, and you have counted the multiples of 10 twice.

Divide that answer by 1000 to get the probability.