Primary 3 · Measurement & Geometry

P3 time

In P3, your child finds how long something lasts, its duration, and works out a starting or finishing time from the other two. They also measure short times in seconds and read and write the 24-hour clock.

Taught in
Term 4
Syllabus
3 skills
Usual slip
Subtracts the times

A timeline from 10 40 to 12 25 counted on in three stages

What your child learns in P3 time

Three skills, each with what it looks like on a worksheet.

Follows the latest (2026) MOE syllabus
See the syllabus wording
  • measuring time in seconds
  • finding the starting time, finishing time or duration given the other two quantities
  • 24-hour clock

Start, finish and how long

Given two of the three, your child finds the third on a timeline. Count on to the next hour, then the whole hours, then the minutes left. For a starting time, count back the same way.

SpanGap
10 40 → 11 0020 min
11 00 → 12 001 h
12 00 → 12 2525 min
10 40 to 12 25 is 1 h 45 min

The 24-hour clock

The 24-hour clock counts the hours straight through the day, from 00 00 at midnight to 23 59. From 1.00 p.m., add 12 to the hour, so 4.30 p.m. is 16 30. Morning times keep their hour.

12-hour clock24-hour clock
8.15 a.m.08 15
12.00 noon12 00
4.30 p.m.16 30
11.45 p.m.23 45
The same times, two ways

Seconds

Seconds measure short times, like a race or a lift ride. 60 seconds make 1 minute, just as 60 minutes make 1 hour. That 60 is why times are counted on, not subtracted like ordinary numbers.

Is the same as
1 minute60 seconds
1 hour60 minutes
1 day24 hours
60 seconds, 60 minutes, 24 hours

Key facts and formulas

Term 4
  • Seconds60 seconds make 1 minute.1 min 15 s=1\,\text{min}\ 15\,\text{s} = 60 s+15 s=60\,\text{s} + 15\,\text{s} = 75 s75\,\text{s}
  • 12-hour24-hour
    9.05 a.m.09 05
    12 noon12 00
    3.15 p.m.15 15
    midnight00 00
    24-hour clockAfter 12 noon, add 12 to the hour. Midnight is 00 00.3.15 p.m.=3.15\text{ p.m.} = 15 1515\ 15
  • SpanGap
    9.45 a.m. → 10 a.m.15 min
    10 a.m. → 11 a.m.1 h
    11 a.m. → 11.15 a.m.15 min
    How long it takesCount on to the next hour, then the whole hours, then the minutes left.9.45 a.m. to 11.15 a.m. → 15 min+1 h+15 min=15\,\text{min} + 1\,\text{h} + 15\,\text{min} = 1 h 30 min1\,\text{h}\ 30\,\text{min}
  • ClockTime
    startread from the hands
    ClockTime
    endread from the hands
    Start time and end timeEnd time = start time + how long. Start time = end time − how long.2.40 p.m.+50 min=2.40\text{ p.m.} + 50\,\text{min} = 3.30 p.m.3.30\text{ p.m.}3.30 p.m.−50 min=3.30\text{ p.m.} - 50\,\text{min} = 2.40 p.m.2.40\text{ p.m.}

Words to know

Duration
How long something lasts, from its starting time to its finishing time.
Count on
Find a duration by moving forward from the starting time in stages, never by subtracting.
24-hour clock
Times written with four digits from 00 00 to 23 59, with no a.m. or p.m.

The sentence that costs the mark

How long is it from 3.50 p.m. to 4.20 p.m.?

What the working usually does

subtract3.50, 4.20=70 min

Subtracts as if minutes ran to 100, reading 4.20 − 3.50 like 420 − 350. But an hour is 60 minutes.

What the question asked

count on3.50, 4.20=30 min

Counts on in two hops: 3.50 to 4.00 is 10 minutes, then 4.00 to 4.20 is 20 more. 10 + 20 = 30.

Subtracting is how you find the difference between ordinary numbers, so it feels right for clock times too. But time runs in 60s, not 100s. Cross to the next hour first, then count the rest, and the 70 becomes 30.

The same P3 time question, worked properly

Lah works through it the way she does every question in StudyLah: one step at a time, marking the picture as she goes.

George reached the library at 14 15. He left the library at 16 05. How long was he at the library?

Step 1 of 5▌
  1. He was there from 14 15 to 16 05. Count on to the next hour first: from 14 15 to 15 00 is 45 minutes.
  2. An hour has 60 minutes, so count the whole hour next: from 15 00 to 16 00 is 1 hour.
  3. Then from 16 00 to 16 05 is 5 minutes.
  4. 45 minutes and 5 minutes make 45 + 5 = 50 minutes. With the 1 hour, that is 1 h 50 min.
  5. So George was at the library for 1 h 50 min.

Every question in StudyLah comes with a walkthrough like this one.

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Three quick P3 time questions

Try them together, then tap to check.

Question 1

Daniel began his tuition class at 15 50. It lasted 1 h 25 min. What time did the class end?

Show answer

Answer17 15. One hour after 15 50 is 16 50. Then 10 minutes reach 17 00, and 15 more make 17 15.

Question 2

Change 7.50 p.m. to 24-hour time.

Show answer

Answer19 50. From 1.00 p.m. on, add 12 to the hour, 7 + 12 = 19. The minutes stay as 50.

Question 3

Wei Ming timed the lift in his HDB block. The table shows his stopwatch when the lift started and when it stopped. How many seconds did the lift take?

Time shown
When it started09:41:12
When it stopped09:41:47
Show answer

Answer35 seconds. Both readings show 09:41, so only the seconds change, from 12 to 47, and 47 − 12 = 35.

Helping at home

How to tell it has clicked

Ask how long from 3.50 p.m. to 4.20 p.m. If the times are lined up and subtracted to get 70, that is the slip. If your child jumps to 4.00 first and then adds the rest, they have it.

For the 24-hour clock, ask for 9 in the morning. A child who writes 21 00 is adding 12 to every hour, not only the ones after noon.

Try this tonight

Use the kitchen clock. At 3.50, ask how long until 4.20, and count it on the face: jump to 4 o'clock first, then the extra minutes.

Read the MRT or bus times aloud in both forms. 18 20 is 6.20 p.m.; say both until switching is easy.

Before and after P3 time

  1. Builds on

    Primary 2 Time

    Converts hours to minutes, using 60

  2. You are here

    Primary 3 Time

    Finds durations and reads the 24-hour clock

  3. Leads to

    Primary 5 Rate

    Uses an amount per unit to find totals

The methods your child will use here

More in Primary 3

Struggling with the working rather than the topic itself? How to help your child with problem sums

See how your child is doing on this topic

StudyLah marks each step separately, so you can see whether it was the setup or the arithmetic that cost the mark.

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