The analysis process is as follows:
You only lose 5 points when you do it. If you do something wrong, you will not only lose 5 points, but also deduct 2 points, which is equivalent to losing 5+2 = 7 points. And (100-64)÷7 can't be divided, which proves that he didn't do it.
So suppose he didn't take the A road and took the B road by mistake.
5a+7b= 100-64=36
Because both A and B are integers, A = 3 and B = 3.
Then he answered the question 20-3-3 = 14 correctly.
Extended data
Integer addition is one of the basic addition operations. Addition is to combine more than two integers into one number, and the result is called sum. The addition symbol is the plus sign (+). Connect items with a plus sign when adding. Put and after the equal sign (=). Example: If the sum of 1, 2 and 4 is 7, it is written as 1+2+4=7.
Integer subtraction rules are expressed in three cases:
1, one digit or two digits MINUS one digit, the difference is the subtraction rule of one digit. According to the relationship that subtraction is the inverse operation of addition, the addition table can be used for calculation.
2. Multi-digit subtraction rules. The same numbers are aligned from one digit. If the number of digits is not reduced enough, borrow one from the previous number and then reduce it.
3. For any number A, there are always a-a=0, a-0=a, and 0-0=0.