Assuming all the questions are done correctly, 20 questions should get 20x5= 100. Now it's only 36 points, 64 points short.

1 question 5 points, wrong question 3 points, difference 8 points. 64÷8=8, which means eight questions are wrong.

20-8= 12.* * * Get 12 right 8 wrong.

Checking calculation: 12x5=60, 8x3=24, 60-24=36.

Method 2: Solving the column equation.

Solution: Suppose Xiaoming did the X problem correctly. What I did wrong was question 20-X.

5x-3(20-x)=36

5x-60+3x=36

8x=96

x= 12

A: Xiao Ming got it right 12.

These two methods are both primary school solutions.