Question

How many numbers are there between $100$ and $1000$, such that $5$ is in the units place?

Answer 1

Choose the hundreds digit 9 ways, $1,2,3,4,5,6,7,8,9$

Choose the tens digit 10 ways, $0,1,2,3,4,5,6,7,8,9$

Choose the units digit 1 way, 5.

Answer $9\times 10\times 1=90$ ways