measurement · Year 4 · AC9M4M03
Elapsed time
Elapsed time is how long passes between a start time and a finish time. Because an hour has 60 minutes, not 100, you cannot just subtract the digits. Count up in two hops instead: first to the next o'clock, then on to the finish. From 3:50 to 4:10, it is 10 minutes up to 4:00 and 10 minutes more to 4:10, which is 20 minutes altogether. When the minutes seem to go backwards, it is a sign the hour has rolled over.
Sample questions
A lesson starts at 3:45 and finishes at 4:20. How many minutes long is it?
- From 3:45, count up to 4:00 — that is 15 minutes.
- Then on to 4:20 is 20 more minutes.
- Elapsed time = 35 minutes.
Answer: 35
A lesson starts at 8:55 and finishes at 9:15. How many minutes long is it?
- From 8:55, count up to 9:00 — that is 5 minutes.
- Then on to 9:15 is 15 more minutes.
- Elapsed time = 20 minutes.
Answer: 20
A lesson starts at 7:45 and finishes at 8:20. How many minutes long is it?
- From 7:45, count up to 8:00 — that is 15 minutes.
- Then on to 8:20 is 20 more minutes.
- Elapsed time = 35 minutes.
Answer: 35