How many integers are there from 9 to 19?

Answer 1

Assuming you include the endpoints (9 and 19, in this case), the calculation you must do is:19 - 9 + 1

If you don't subtract the endpoints (the question would be phrased something like "... between 9 and 19"), you have to subtract one instead of adding one, at the end.

Answer 2

Including 9 and 19 there are eleven of them.

Answer 3

Ten.