8 of them.
There are 800 such numbers.
19 of them do.
There are 45 of them.
8 ... they are 20, 30, 40, etc on up to 90
Only one positive prime number has a 5 in the ones digit. That prime number is 5. All other numbers with a 5 in the ones digit are composite because they will be divisible by 5.
The answer depends on what the tens digit is greater than, and what the ones digit does then.
13
The ones digit in even numbers can be any of the following: 0, 2, 4, 6, or 8. This is because even numbers are divisible by 2, meaning they can be expressed as 2 multiplied by another integer. The ones digit is the digit in the ones place of a number, which can range from 0 to 9.
505
505
421 and 842
Hint, but not your answer: You know your answer has to be between 11 and 99. Furthermore, it has to be a square. One, two, and three when squared are still single digit numbers. Four squared is 16, which is not squaring the ones digit. Keep going...