1. Ten-fold method:

13-8=3+ 10-8=3+2=5

Divide the minuend into several+10, and subtract the minuend from 10.

2. Ten-level method:

13-8= 13-(3+5)= 10-5=5

Divide the subtraction into the sum of two numbers, one of which has the same addend as the minuend, so that the number subtracted by the subtraction becomes 10, and then subtract it.

Both methods convert the subtraction within 20 into the subtraction within 10 by splitting.

Extended data

Additive commutative law: A+B = B+A.

Additive associative law: a+(b+c) = (a+b)+c.

Multiplicative commutative law: a*b=b*a

Law of multiplicative association: a*(b*c)=(a*b)*c

Multiplication and distribution law: a*(b+c)=a*b+a*c

The essence of continuous reduction: a-b-c=a-(b+c)

References:

Baidu encyclopedia-elementary mathematics