Question

What are the factors of 15900

Answer 1

well, certainly 10* 10 * 159 = 5*2*5*2 * 159

now what can you do with 159?
try 3
3 * 53
what can you do with 53?
nothing :(
so
2*2*5*5*3*53

Answer 2

With 2 zeros at the end, you can start with factors of 100: 50, 25, 10, 5, 4, 2.