There is only one number called a single digit, such as 1, 2. A number with two numbers, such as 1 1, count it, two numbers.

The addition within 100 can basically be regarded as the combination of 1-2 additions, one at a time and ten at a time. Let's talk about the quick calculation formula, especially the quick calculation formula with carry.

9+ 1, carry+1 minus 9; 9+2, carry+1, the last digit minus 8; 9+3, carry+1 finally minus 7;

9+4, carry+1 finally minus 6; 9+5, carry+1 and finally subtract 5; 9+6, carry+1 and finally subtract 4;

9+7, carry+1, and subtract 3 from the last digit; 9+8, carry+1, and subtract 2 from the last digit; 9+9, carry+1 last digit minus1;

Let's briefly explain this formula. For example: 19+37, which is 9+7 in the unit, then the tenth place is+1 (the tenth place becomes 1+3+ 1=5), and it is -3(9-3=6) in the unit, and finally it is calculated.

It is convenient to expand the information formula, but it also needs students to remember it in actual combat. To remember the formula, you need to know the principle of the formula in order to understand it better.

Here, let's take 17+37 as an example. First, we decompose this formula:

17+37= 17+(30+7)= 17+(30+ 10-3)= 17+40-3=50+(7-3)=54

We can find that this formula is actually a disassembly method, which decomposes the second addend into a unit part and a tenth part, and then decomposes each part into the difference between 10 and another number. Then reassemble to get the final result.