Hi Beth,

First I would make sure that your child knows the the digits are 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.

Since the ones digit is not 0 the smallest it can be is 1. Since the tens digit is 8 more than the ones digit in this case the tens digit would be 1 + 8 = 9 so the number 91 is a correct answer.

Is there any other correct answer? What if the ones digit is 2 then the tens digit would be 2 + 8 = 10 but 10 is not a digit. Likewise if the ones digit is 3 then the tens digit would have to be 3 + 8 = 11 which is not a digit. What you see is that if the ones digit is larger than 1 then 8 plus the tens digit is not a digit and hence 91 is the only correct answer.

I hope this helps,
Penny