What is the least multiple of 15 whose digits consist only of 1's and 0's?

Remark
Fun question. It has to have at least three 1s in it. that's because it has to be divisible by 3 and 5. So to get it divisible by 3 you need to have something that will add up to 3 or 3n where n is any number above 0.

The 5 part comes into it by adding a zero on the end. Something divisible by 5 must and in 0 or 5. Since 5 is not permitted, the number has to end in zero.

Answer. The Smallest number must be 1110