Page 144 - Start Up Mathematics_4

If the given time is between 1300 hours to 2359 hours, subtract 1200 hours and add
p.m. to it.

Examples, 1350 hours – 1200 hours = 01:50 p.m. 1620 hours – 1200 hours = 04:20 p.m.
Look at some more examples.

Example 2: Convert the given 12-hour time to 24-hour time.
(a) 2:15 p.m. (b) 7:45 p.m. (c) 9:20 a.m.

Solution: (a) 2:15 p.m. = 0215 hours + 1200 hours = 1415 hours or 14:15
(b) 7:45 p.m. = 0745 hours + 1200 hours = 1945 hours or 19:45

(c) 9:20 a.m. = 0920 hours or 09:20
Example 3: Convert the given 24-hour time to 12-hour time.

(a) 15:00 (b) 18:40 (c) 10:10 (d) 22:25
Solution: (a) 15:00 = 1500 hours = 1500 hours – 1200 hours = 0300 hours = 3:00 p.m.

(b) 18:40 = 1840 hours = 1840 hours – 1200 hours = 0640 hours = 6:40 p.m.
(c) 10:10 = 1010 hours = 10:10 a.m. (as time is less than 1200 hours)
(d) 22:25 = 2225 hours = 2225 hours – 1200 hours = 1025 hours = 10:25 p.m.

Advantages of 24-Hour Clock over 12-Hour Clock

1. There is less confusion between morning and evening. For example, 6 o’clock does
not clarify the time of the day whereas 1800 hours is clearly an evening time.
2. 2400 is clearly midnight and 1200 is noon without confusion.

3. It is easier to calculate duration. For example, it is not so easy to calculate that
09:30 a.m. to 2:30 p.m. is 5 hours whereas, it is easier to calculate that 0930 hours to
1430 hours is 5 hours.

EXERCISE 10.3

1. Convert the given 12-hour time to 24-hour time.
(a) 1:20 p.m. (b) 2:19 a.m. (c) 11:15 a.m. (d) 3:40 p.m.

(e) 5:45 p.m. (f) 7:05 p.m. (g) 10:55 a.m. (h) 8:50 p.m.
2. Convert the given 24-hour time to 12-hour time.

(a) 1100 hours (b) 1320 hours (c) 1418 hours (d) 1635 hours
(e) 1725 hours (f) 1945 hours (g) 2010 hours (h) 2340 hours

3. Write the time in 12-hour and 24-hour system.
12-hour clock 24-hour clock

(a) Arpita ate her breakfast at 8 o’clock.

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