First, addition

1, two numbers add to keep the number unchanged: if one of the two added numbers increases, the other decreases, one increases and the other decreases.

When two numbers are added, one of them remains the same. If another number changes, this number will also change, and the result will change as much as the addend.

3. Add the two numbers and exchange positions to get the same number.

Second, subtraction.

1, one number subtracts another number, keeping the reduction unchanged: if the minuend increases, the result also increases, and the result increases as much as the minuend increases; When the minuend is reduced, the result is also reduced, and the result is also reduced by how much the minuend is.

2. Subtract one number from another to keep the minuend unchanged: if meiosis increases, the result will decrease, and the result will decrease as much as meiosis increases; If meiosis decreases, the results increase, and the results increase by how much meiosis decreases.

3. Subtract one number from another and keep this number unchanged: the minuend will increase as much as it increases; As much as the minuend is reduced, the minuend will also be reduced.

Formula: Addendum+Addendum = sum, Addendum = sum-another Addendum, Minus = Minus+Difference, Minus = Minus-Difference, Difference = Minus-Minus.

Extended data:

Let children learn to count skillfully. Count down from "1" skillfully; Can skillfully count from a certain number in the middle. For example, you say: count from 4; Starting from 12; Can skillfully count down from a middle number. For example, you said: Count backwards from 4, and count backwards from 12.

Counting is the earliest thing children learn, and we think every child should know it. However, we ignore that many children only start counting from "1". If you ask him to count from a number in the middle, they may not know how to count.