Question

I am a number between 70-90 my tens digit is two less than my ones digit I am a
prime number what am I

Answer 1

If tens digit is two less than ones digit, then ones digit is 2 greater than the tens digit.

The tens digit can be 7 , 8 or 9.

You should discard 8 and 9 because for tens digit 8 the once digit is 10 and for tens digit 9 the once digit is 11.

For a two-digit number that is impossible.

So the tens digit is 7.

It is two less than 9.

So your number is 79.