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Conversion of 12-hour Clock Time to 24-hour Clock Time
In order to convert a time of the 12-hour clock format to the 24-hour clock format,

remember these rules.

rule examples

For a time from 12:00 midnight to a. 12 midnight = 00:00 hours
12:59 a.m., subtract 12 hours and write the b. 12:36 a.m. = 00:36 hours

time without a.m. c. 12:59 a.m. = 00:59 hours

For a time from 1:00 a.m. to 12:59 p.m., a. 1:00 a.m. = 01:00 hours
do not change the number. Write the time b. 10:40 a.m. = 10:40 hours
without a.m. or p.m. c. 12 noon = 12:00 hours

d. 12:59 p.m. = 12:59 hours

For a time from 1:00 p.m. to 11:59 p.m., a. 1:00 p.m. = 13:00 hours
add 12 hours and write the time without b. 8:24 p.m. = 20:24 hours
p.m. c. 11:59 p.m. = 23:59 hours

example 2. Convert the following according to the 24-hour clock format.

a. 5:37 p.m. b. 12:21 a.m. c. 3:30 a.m.

d. 7:58 p.m. e. 9:42 p.m. f. 11:59 p.m.
Solution. a. 5:37 p.m. = 17:37 hours b. 12:21 a.m. = 00:21 hours

c. 3:30 a.m. = 03:30 hours d. 7:58 p.m. = 19:58 hours

e. 9:42 p.m. = 21:42 hours f. 11:59 p.m. = 23:59 hours

Exercise 10A

1. Write the time using a.m., p.m., noon or midnight.
a. 05:40 hours b. 01:20 hours c. 00:20 hours d. 12:29 hours

e. 11:30 hours f. 16:40 hours g. 16:25 hours h. 00:00 hours
i. 22:22 hours j. 21:38 hours k. 13:48 hours l. 20:00 hours

2. Convert the following into 24-hour clock time.
a. 6:05 a.m. b. 10:24 a.m. c. 12:06 a.m. d. 7:36 p.m.

e. 12:15 p.m. f. 2:17 p.m. g. 11:00 p.m. h. 4:57 a.m.
i. 12:00 midnight j. 1:40 a.m. k. 3:30 p.m. l. 9:40 p.m.

220 Mathematics 5