There are five algorithms for grade one 17-9, as follows:

1, use 17 = 10+7,17-9 = 7+10-9 = 7+1= 9.

2. Reciprocal addition and subtraction: 9+8 = 17, 17-9 = 8.

3. Ten plus 1 method: divide 10 into 9 and 1, and then add 1 to another number.

4. Digital addition: for example, 17-9 = 10-9+7 = 8.

5. Rounding method:17-9 =17-7-2 =10-2 = 8

Subtraction of abdication:

Subtraction is a mathematical term, which can also be called borrow subtraction. So when you subtract two numbers, if the last digit is not enough, borrow it, then add 10, and then calculate.

5 from 24 to 15, 15 minus 24 equals 1, minus 10 equals 9, which is a bit, and the decimal digit is borrowed, so the decimal digit is now 1 minus 1, which is 0. If ten continue to shrink back, repeat.