How many numbers are there that have only 3 tens

I saw this problem somewhere over the rainbow and it is quite confusing, especially for preschoolers and their parents who are not that into maths. 

Allow me to guide you on how to solve this problem.

Question: 

How many numbers are there that have only 3 tens?

Solution:

The numbers that have three tens are numbers in the thirties. These are 30, 31, 32, 33, 34, 35, 36, 37, 38, and 39.

The number 40 has already 4 tens so we can no longer count more than 39.

30 -> exactly three tens

31 -> 3 tens and 1 one.

32-> 3 tens and 2 ones.

You get the idea.

Therefore, the answer to this question is 10.