The order you add the numbers doesn't matter. Look at these examples:
ORIGINAL EXPANDED ADD LAST ANSWER PROBLEM VERSION TWO VALUES 52 + 9 = 50 + 2 + 9 = 50 + 11 = 61 39 + 4 = 30 + 9 + 4 = 30 + 13 = 43 21 + 9 = 20 + 1 + 9 = 20 + 10 = 30 68 + 5 = 60 + 8 + 5 = 60 + 13 = 73