Calculating elapsed time can be tricky. Our number system is based on tens, and we typically calculate and regroup using a system of tens. Time, on the other hand, involves 60 minutes in 1 hour, and hours are counted up to 12 before starting over from 1. Our normal system of adding and subtracting using groups of tens will not work.
A game starts at 2:10 pm and ends at 4:45 pm. How long did the game last?
A chart can be used to count up the hours and minutes.