Elapsed time between two clock times

3.MD.A.12.MD.C.7 · take · grade 3

Archetype: Elapsed Time and Base-Sixty Regrouping · step in a 10-type progression

▶ Practice — 8 problems

A workout started at 1:20 and ended at 2:40. How long did the workout take, in hours and minutes?

Show solution

Understand

A workout began at 1:20 and ended at 2:40. Find how long it lasted, in hours and minutes.

Givens

Start time is 1:20.
End time is 2:40.
The figure shows a start clock at 1:20, an end clock at 2:40, and a time band below split into 10-minute cells from 1:20 to 2:40.

Unknowns

The elapsed time from 1:20 to 2:40 in hours and minutes.

Constraints

End time is later than start time on the same afternoon.

Plan

#1 Draw a Diagram · also uses: #7 Identify Subproblems

Use the time band as a number line: jump from 1:20 to 2:20 (a whole hour), then from 2:20 to 2:40 (the remaining minutes). Adding the two jumps gives the total elapsed time.

Execute

#1 Draw a Diagram 3.MD.A.1

From 1:20 to 2:20 is exactly 1 hour.

1{:}20 \to 2{:}20 = 1 \text{ hour}

Moving the hour by one and keeping the same minutes is a clean 1-hour hop on the time line.

#7 Identify Subproblems 2.MD.C.7

From 2:20 to 2:40 the minute hand moves from 20 to 40, which is 20 minutes.

40 - 20 = 20 \text{ minutes}

Same hour, so just subtract the minute numbers to get the extra time.

#7 Identify Subproblems 3.MD.A.1

Total elapsed time is 1 hour plus 20 minutes.

1 \text{ hour} + 20 \text{ minutes} = 1 \text{ hour } 20 \text{ minutes}

Combining the whole-hour jump and the minute jump gives the full duration.

Answer: 1 hour 20 minutes

Review

Check by adding the duration back to the start: 1:20 + 1 hour = 2:20, then + 20 minutes = 2:40, which matches the end time. So 1 hour 20 minutes is correct.

Count in 10-minute cells on the time band: from 1:20 to 2:40 there are 8 cells of 10 minutes = 80 minutes = 1 hour 20 minutes.

Standards · min grade 3

3.MD.A.1 Tell and write time to the nearest minute and solve elapsed time problems — Finding the elapsed time from 1:20 to 2:40 by adding a whole-hour jump and a minute jump.
2.MD.C.7 Tell and write time from analog and digital clocks to nearest five minutes — Reading the start and end clock times and subtracting minutes within the same hour.

💡 Hop one whole hour, then count the extra minutes: easy Grade 3 elapsed-time counting!