Measurement and Data
Time and how long things last
Work out how long something lasts, including when it runs past the hour, and find a start or finish time from a duration.
Working out how long something lasts is subtraction, but not the kind you can do in columns — there are sixty minutes in an hour, not a hundred, so 10:05 take away 9:20 is not 85 of anything. The safe method is to count forwards in stages, using the whole hours as stepping stones.
Hop to the hour first
From 9:20 to 10:05, hop to 10:00 first — that is 40 minutes — and then carry on the last 5. Forty and five is forty-five. Doing it in one jump is where mistakes come from; doing it in hops past each whole hour is where they do not.
Worked example
A film starts at 3:00 pm and ends at 4:45 pm. How long is it?
From 3:00 to 4:00 is one whole hour, which is 60 minutes.
The first hop lands on the next whole hour.
Try it together
Now let us time a train from 6:50 am to 9:20 am together.
Three hops: up to the next whole hour, then across the whole hours, then the last few minutes.
1.How many minutes is it from 6:50 to 7:00?
Have a go
Have a go on your own: a lesson runs from 11:40 am to 12:25 pm. How many minutes long is it?
Hint: Hop up to twelve o'clock first.
Ready to practice?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.