what you do is look at the numbers in order from the greatest number, to the least. For example, in this problem, we would start with the 5 in 513251, and the 5 in 513521. Since they are both fives, we don't know yet which one is bigger. So we move onto the next number, which would be the 1 in 513251, and the 1 in 513521. They are both the same, so we go onto the 3 in 513251, and the 3 in 513521. Those are also both the same, to we go onto the 2 in 513251, and the 5 in 513521. As you can see, the 5 from 513521 is greater then the 2 in 513251, so that shows that 513521 is greater.