IGCSE · Practice questions · Time: 12- and 24-hour clock, time calculations

Count on in steps.

Six original Cambridge-style questions on time: 12- and 24-hour clocks, intervals, timetables and time zones.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

The method

Count on, in base 60.

24-hour clock: four digits; add 12 for p.m. times after 1 p.m.
Intervals: count on to the next hour, then whole hours, then minutes.
Decimal hours: decimal part × 60 gives minutes.
Timetables: read down one column for one journey.
Time zones: 'ahead' means add the difference; 'behind' means subtract.

Recall

[2 marks]

(a) Write 7.05 p.m. in the 24-hour clock. (b) Write 00 25 in the 12-hour clock.

(a) 19 05 ✓
(b) 12.25 a.m. ✓

Recall

[1 marks]

How many seconds are there in one day?

\(24 \times 60 \times 60 = 86\,400\) seconds ✓

Calculation

[2 marks]

A film starts at 18 50 and lasts 2 hours 25 minutes. At what time does it finish? Give your answer in the 12-hour clock.

18 50 + 2 h = 20 50; 20 50 + 25 min = 21 15. ✓
21 15 is 9.15 p.m. ✓

Calculation

[2 marks]

Write 2.4 days in hours and minutes.

\(2.4 \times 24 = 57.6\) hours. ✓
\(0.6 \times 60 = 36\) minutes, so 57 hours 36 minutes. ✓

Analysis

[3 marks]

Part of a bus timetable is shown.

Stop	Bus A	Bus B	Bus C
Station	06 50	07 35	08 20
Market	07 06	07 51	08 36
Hospital	07 23	08 08	08 53
Airport	07 58	08 43	09 28

(a) How long does Bus A take from the Station to the Airport?
(b) Pia arrives at the Hospital stop at 07 30. She takes the next bus to the Airport. How long after arriving at the Hospital stop does she reach the Airport?

(a) 06 50 to 07 58 is 1 hour 8 minutes. ✓
(b) The next bus from the Hospital is Bus B at 08 08, reaching the Airport at 08 43. ✓
07 30 to 08 43 is 1 hour 13 minutes. ✓

Analysis

[3 marks]

A plane leaves Sydney at 10 45 local time on Monday. It lands in Los Angeles at 06 15 local time on the same Monday. Los Angeles time is 18 hours behind Sydney time.

Calculate the flight time.

Change the landing time to Sydney time: 06 15 Monday + 18 h = 00 15 Tuesday. ✓
10 45 Monday to 00 15 Tuesday: 10 45 to 24 00 is 13 h 15 min, plus 15 min. ✓
Flight time = 13 hours 30 minutes. ✓

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