First of all, we should understand why we should borrow decimals with the same number and subtract large numbers. If it's not enough, borrow the last one. Two soldiers A and B fought, but they were too weak to beat them, so they went to their superiors for help.

Example: 33-8, where 3 is less than 8, you need to borrow one forward.

Second, we should know how to borrow. The latter must learn from the former.

For example: 36-9, 6 of the digits needs to borrow one from 3 of the digits.

Then we should understand that the borrowed number is used as 10. Just like A's superior is a class, and a class called A has 10 people.

Example: 27-8, the number 7 borrows the number 10, and it becomes 17 minus 8.

Finally, the borrowing number is one less 1.

Example: 47- 18. After borrowing, the unit is 7, which becomes17; The first four digits of the ten digits borrow 1 to become three digits;

The unit is17-8 = 9; The tenth digit is 3- 1 = 2 and the answer is 29.