Question

Find the smallest natural number that is a multiple of 45 and where all of its digits are zeros and ones.

Answer 1

1111111110

Explanation:

45 is 9, and 5.

9 divisibility rule: Digits have to add up to 9.

We know this has to be 1's and 0's.

So there has to be 9 1's.

111111111.

5 divisibility rule: Last digit has to be 0 or 5.

1111111110 will be our final answer.

Wait- let's check if it's divisible. Using a calculator, this determines it does work.

Enjoy.