If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below 1000.
- Prepare a list with all the multiples of 3 below 1000
- Prepare a list with all the multiples of 5 below 1000, but
- filter out everything that divides by 3
- Sum each list and then sum the sums.