Method 1: 10 plus 7.

7 adds up to 10. If it is short of 3, you can divide 8 into 3 and 5. Calculate 7+3 to get 10, and then calculate 10+5.

Formula: 7+8=(7+3)+5= 15.

Method 2: 10 plus 8.

8 adds up to 10. If 2 is missing, 7 can be decomposed into 2 and 5. Calculate 2+8 to get 10, and then 10+5.

Formula: 7+8=5+(2+8)= 15.

Extended data:

Simple mathematical calculation is one of the necessary abilities for children from kindergarten to primary school. Because preschool children have not established the concept of number, it is difficult to learn addition and subtraction in mathematics. It is a gradual process for children to learn addition and subtraction.

Ten-complement method is a problem-solving method often used by children when they are beginners in mathematical operation and addition. The idea is very simple, that is, take 10 as the standard, make up a few differences, make up a few losses, and then add up. "9 ratio 1", "8 ratio 2", "7 ratio 3", "6 ratio 4" and "5 ratio 5" are his memory formulas.