Calculate first.

If the two numbers add up, if they can add up to exactly ten, one hundred, one thousand, ten thousand ... then calculate first.

For example,1+9 =10,3+7 =10,2+8 =10,4+6 =10,5+5 =10.

Another example is:12+88 =100,35+65 =100,21+79 =100,44+56 =100.

In the above formula, 1 is called the "complement" of 9; 79 is called the "complement" of 2 1, and 44 is also called the "complement" of 56, which means that two numbers are "complements" of each other.

One digit of extended data+one digit =2 digits. For example: 4+7= 1 1

Although this involves the contents of one digit and ten digits, because it is one digit plus one digit, you don't have to consider the position, and because you can skillfully remember the numbers within 20, you can write the answer directly according to the previous method.

One digit+two digits = two digits (no carry) Example: 6+ 12= 18.

Pay attention to the position of this. But this does not involve carry and abdication, so just let the children distinguish between 1 and 10, pay attention to the position, and then follow the previous method.

One digit+two digits = two digits (carry), for example: 8+ 13=2 1.

On the basis of "3", teach children to move in ten directions 1, and pay attention to counting one first, then dozens.

Subtraction is also suitable. You can also use tools such as arithmetic sticks to help children understand.