You can divide the apples by 2, but you will have a decimal. The closest you can get it without having a decimal is 7 in one pile, and 6 in the other. The pile with 7 apples is bigger.
The big pile has 7 apples because 13÷2 will leave you with a remainder so if you split 13 apples, 1 apple would be left, so then you add it to one of the piles to get 7 in one pile and 6 in the other.
