The football team has jerseys numbered from 10 to 30. Everyone gets a jersey, and there are three leftover. How many people are on the football team?

[math_celebrity]

The formula for inclusive number counts from A to B is:
B - A + 1
With B = 30 and A = 10, we have
30 - 10 + 1
21

We're told everyone gets a jersey and there are 3 left over.
21 - 3 = 18 people on the team