Page 132 - Math Skill - 5
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130 Maths
The 12-hour clock system can cause confusion if the time is not followed by a.m. or p.m. The
24-hour clock gives correct time. In this system, the time of the day is given as hhmm, where hh
stands for the hours past midnight and mm stands for the number of minutes past that hour.
For example,
The day starts at midnight which is 0000 hours.
0015 hours → 15 minutes past midnight or 12:15 a.m.
1215 hours → 15 minutes past noon or 12:15 p.m.
1300 hours → 1:00 p.m.
1830 hours → half past six or 6:30 p.m.
Converting 12-hour clock Time to 24-hour clock Time
To convert the a.m. time to the 24-hour clock, we write 12-hour clock 24-hour clock
the hour as a 2-digit number and remove the colon. 6:00 p.m. 1800 hours
For example, 2:00 a.m. in the 12-hour clock is written as
0200 hours in the 24-hour clock. 4:15 p.m. 1615 hours
To convert the p.m. time to the 24-hour clock, we add 3:45 a.m. 0345 hours
12 to the hours. 7:30 a.m. 0730 hours
For example, 2:00 p.m. in the 12-hour clock is written as 1400 hours in the 24-hour clock.
Converting 24-hour Clock Time to 12-hour clock Time
To convert 24-hour clock time to 12-hour clock time, we do as follows:
(i) If the 24-hour clock time is less than 12, then we put a colon after the hours digits and write
the time in a.m.
(ii) If the 24-hour clock time is greater than 12, then we subtract 12 hours from the hours and
write the time in p.m.
24-hour clock 12-hour clock
0030 hours 12:30 a.m. Fact-o-meter
0400 hours 4:00 a.m. If the time in 24-hour clock
has 00 time, then the time
1640 hours 4:40 p.m. in the 12-hour clock will be
1940 hours 7:40 p.m. 12:00 midnight.
Exercise 10.1
1. Convert to 12-hour clock time.
(a) 0000 hours (b) 1605 hours (c) 0843 hours
(d) 1530 hours (e) 2250 hours (f) 1235 hours
