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Academy11+

11+ Maths · Topic explained

Time

A film starts at 18:45 and ends at 20:20. How long is it?

The big idea

Time works in 60s, not 100s: count on in hops to the next hour.

Picture it

Hop along a timeline: to the hour, then whole hours, then the minutes left.

Key words

am and pm
am is before midday, pm is after midday.
24-hour clock
Counts 00:00 to 23:59; for pm times add 12 to the hour.
duration
How long something lasts.

Worked examples

  1. 1Warm-up

    Write 4:30 pm in the 24-hour clock.

    • pm, so add 12 to the hour: 4 + 12 = 16
    • 16:30
  2. 211+ standard

    A film starts at 18:45 and ends at 20:20. How long is it?

    • 18:45 → 19:00 is 15 min
    • 19:00 → 20:00 is 1 h; 20:00 → 20:20 is 20 min
    • 15 min + 1 h + 20 min = 1 h 35 min
  3. 311+ standard

    Buses leave every 25 minutes, starting at 07:40. When does the third bus leave?

    • 1st: 07:40
    • 2nd: 07:40 + 25 min = 08:05
    • 3rd: 08:05 + 25 min = 08:30
  4. 411+ standard

    How many minutes are there in 2¾ hours?

    • 2 hours = 120 minutes
    • ¾ of an hour = 45 minutes
    • 120 + 45 = 165 minutes

The common mistake

The mistake

20:20 − 18:45: 2020 − 1845 = 175, so 1 hour 75 minutes.

Instead

Count on in hops: 15 min + 1 h + 20 min = 1 h 35 min.

Why: An hour has 60 minutes, not 100, so ordinary column subtraction gives the wrong answer.

Where it comes up in the 11+

Timetables, durations across the hour, and 12-hour to 24-hour changes.

The video

Video coming soon

We're making a short video that explains time step by step. Until then, everything it covers is on this page.

Free printable

Time worksheet

Practice questions on this topic to print and try on paper, at home or on the way to school.

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Quick quiz

Have a go first, then tap to see the answer.

  1. 1. Write 7:15 pm in the 24-hour clock.

    • 07:15
    • 17:15
    • 19:15
    • 21:15
    Show the answer

    19:15

    pm, so 7 + 12 = 19.

  2. 2. How long is it from 09:50 to 11:05?

    • 1 h 15 min
    • 1 h 55 min
    • 2 h 15 min
    • 1 h 5 min
    Show the answer

    1 h 15 min

    09:50 → 10:00 is 10 min, → 11:00 is 1 h, → 11:05 is 5 min: 1 h 15 min.

  3. 3. What is 200 minutes in hours and minutes?

    • 2 h
    • 3 h 20 min
    • 2 h 0 min
    • 3 h 2 min
    Show the answer

    3 h 20 min

    3 hours = 180 minutes, and 200 − 180 = 20.