Subtraction formula table within 20:

Extended data:

To sum up the carry addition within 20, the formula is: "add nine MINUS one, add eight MINUS two, add seven MINUS three, add six MINUS four, and add five MINUS five."

Take "plus nine MINUS one" as an example. "Add nine and subtract one" refers to the addition of a number and 9, and the number minus 1 is the unit of their sum.

For example: 8+9= () take 8 and subtract 1 to get 7, and use 7 as the unit of summation, that is, 8+9= 17, 5+9= () take 5 and subtract 1 to get 4, and use 4 as the unit of summation, that is, 5+9 =/kloc-.

The method of "eight minus two, seven minus three, six minus four and five minus five" is the same as above.

The abdication subtraction within 20 is opposite to the carry addition within 20, that is, the abdication subtraction within 20 is converted into the addition within 10. The formula is: "minus nine plus one, minus eight plus two, minus seven plus three, minus six plus four, minus five plus five.

Take "minus nine plus one" as an example. "Minus nine plus one" refers to a number MINUS nine, and the result of adding 1 to the unit of this number is their difference.

For example, 17-9 = () take the 7th place of 17, and add 1, and the result is 8, that is, 17-9 = 8, 13-9 = () take/kloc-.

For example: 17-2 = () Distinguish which is a single digit and which is a ten digit. First, see if the single digit can be simplified. If 7-2 is simplified enough, subtract it with ten, remember 7 in your mind, then count down 6,5 to get 5, and then 1 of the ten digits remains unchanged, and you will get1.

The method of "minus eight plus two, minus seven plus three, minus six plus four, minus five plus five" is the same as "minus nine plus one".