1. If you subtract two numbers from a number continuously, you can subtract the sum of the two numbers, or you can subtract the first subtraction and then the second subtraction.

For example: 895-342-458 analysis: children's understanding methods.

=895-(342+458) If you calculate the sum of 342 and 158 first, then subtract it at last.

=895-800 is relatively simple and easy.

=95。

2. If you subtract two numbers from a number continuously, you can subtract the first number or the second number first.

For example: 3685-252- 1685.

=3685- 1685-252。

=2000-252。

= 1748。

In the usual study, many children are prone to make mistakes in this problem. Children are influenced by the method 1, so it is not easy to work out "1685-252" first. It should be calculated as: 3685- 1685-252.

Subtraction formula

1, minuend-subtrahend = difference

2. Difference+Minus = Minus

3, the minuend-difference = reduction

Subtraction correlation characteristic

1, inverse exchange rate: subtraction is inverse exchange. If a and b are any two numbers, then (a-b)=-(b-a).

2. Anti-association method: subtraction is anti-association. When trying to redefine subtraction, then a-b-c=a-(b+c).