All the numbers from 10 to 99 are positive 2 digit integers
900 numbers from 100 to 999
There are no pairs of 2-digit numbers with a difference of 90 if both numbers are positive or both negative. However, with one positive and one negative, there are 71 pairs.
There are 320 such numbers.
There are 278 5-digit numbers less than 20,000 that are divisible by both four and nine.
90
90
The 3 digit numbers under 500 are 100 through 499.
149 of them.
4,000 even numbers, 4,000 odd numbers.
There are 294 such numbers.
All the numbers from 10 to 99 are positive 2 digit integers
900 numbers from 100 to 999
There are no pairs of 2-digit numbers with a difference of 90 if both numbers are positive or both negative. However, with one positive and one negative, there are 71 pairs.
102 = 100 which is the first possible three digit number that is a perfect square. 312 = 961 which is the last possible three digit number that is a perfect square. So there are 22 three digit positive numbers that are perfect squares.
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.
An infinite number if you can use positive and negative numbers.