Time

When the school bell rings at "1330", do you know if that means lunchtime or home time? Time questions trip students up not because the maths is hard, but because the clock counts in 60s, not 100s — and there is a whole second way of writing the time. Once you see how the 24-hour clock works and how to count a duration, time becomes one of the most reliable marks on the paper.

Parents: ask your child to predict whether a step adds or subtracts hours before they reveal. The "Method tip" boxes name the exact way a PSLE marker rewards a duration calculation.

By the end you'll be able to read the 24-hour clock, find how long something lasts, read a timetable, and solve start-time and end-time problems. Let's begin.

The 24-hour clock

The 24-hour clock writes the time as four digits, like 0830 or 1500. Instead of starting again at 12, it keeps counting: 1 in the afternoon is 1300, 2 is 1400, and so on up to 2359, just before midnight.

To change an afternoon or evening time to 24-hour form, add 12 to the hour. So 3 pm becomes 3 + 12 = 1500. To go back, subtract 12: 2000 is 2000 − 12 hundred = 8 pm. Morning times stay almost the same: 7 am is 0700.

Finding how long something lasts

The time between a start and an end is called the duration. The safe way to find it is to count up in steps: first to the next whole hour, then the full hours, then the leftover minutes.

For example, from 0940 to 1115: count 20 minutes up to 1000, then 1 hour up to 1100, then 15 minutes up to 1115. Total = 1 hour 35 minutes. Counting in friendly steps stops you from trying to subtract 1115 − 0940 like normal numbers, which goes wrong because minutes only reach 60.

Reading a timetable

A timetable lines up events with their times. To use one, find the row or column you need, then read across or down to the time. Many questions then ask for the duration between two of those times — so you use the counting-up skill again.

For example, if a bus leaves Town at 0850 and reaches the beach at 0935, the journey takes 45 minutes — counted from 0850 up to 0935. Always read the exact times off the table first, then calculate.

Start-time and end-time problems

Two question types come up again and again. If you know the start time and the duration, add the duration to get the end time. If you know the end time and the duration, subtract the duration to get the start time.

For example, a class starts at 1015 and lasts 1 hour 30 minutes: add 1 hour to reach 1115, then 30 minutes to reach 1145, so it ends at 1145. Working backwards, if a show ends at 2030 and lasted 2 hours, subtract 2 hours to get a start of 1830.

Watch out — these are easily mixed up

Quick recap

🎯 Mastery check

Answer all 6 — your progress is saved on this device.

1. What is 9 pm in 24-hour clock time?

   090019002100

2. How long is it from 0815 to 1000?

   1 hour 45 minutes1 hour 15 minutes2 hours 15 minutes

3. A lesson starts at 1130 and lasts 1 hour 20 minutes. What time does it end?

   125012301310

4. A football match ends at 1745 and lasted 90 minutes. What time did it start?

   161516451915

5. A bus leaves at 1255 and arrives at 1340. How long was the journey?

   45 minutes55 minutes1 hour 5 minutes

6. A train timetable shows a train leaving at 0950 and arriving at 1135. A passenger wants the total travel time. What is it?

   1 hour 45 minutes1 hour 85 minutes2 hours 45 minutes

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