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Converting the 12-hour Clock Time to 24-hour Clock Time

rule 1: For the time from 1:00 a.m. to 12:59 p.m., do not change the number. Write the
time without colon (:) sign and instead of a.m. or p.m. write hours.

For example:
(a) 2:00 a.m. = 0200 hours (b) 11:38 a.m. = 1138 hours

(c) 12 noon = 1200 hours (d) 12:58 p.m. = 1258 hours

rule 2: For the time from 1:00 p.m. to 11:59 p.m., add 12:00 hours and write hours
instead of p.m.
For example:

(a) 4:30 p.m. = 1630 hours ( 1200 hours + 0430 hours = 1630 hours)
(b) 9:00 p.m. = 2100 hours ( 1200 hours + 0900 hours = 2100 hours)

rule 3: For the time from 12 midnight to 12:59 a.m., subtract 12:00 hours and write the
time with hours instead of a.m.

For example:
(a) 12:30 a.m. = 0030 hours ( 1230 hours – 1200 hours = 0030 hours)

(b) 12:59 a.m. = 0059 hours ( 1259 hours – 1200 hours = 0059 hours)

example 1: Convert the following 24-hour clock time into 12-hour clock time.
(a) 0025 hours (b) 0604 hours (c) 1328 hours

Solution:

(a) 0025 hours
Here, 0025 hours < 1200 hours.
Therefore, 0025 hours = 00:25 a.m. and 00:25 a.m. = 12:25 a.m.

(b) 0604 hours

Here, 0604 hours < 1200 hours.
Therefore, 0604 hours = 6:04 a.m.
(c) 1328 hours

Here, 1328 hours > 1200 hours
Therefore, 1328 hours = 1328 hours – 1200 hours = 1:28 p.m.

example 2: Convert the following 12-hour clock time into 24-hour clock time.
(a) 3:30 p.m. (b) 4:25 a.m. (c) 12:31 a.m.

Solution:

(a) 3:30 p.m. = 1530 hours ( 1200 hours + 330 hours = 1530 hours)
(b) 4:25 a.m. = 0425 hours ( 0425 hours < 1200 hours 4:25 a.m. = 0425 hours)

(c) 12:31 a.m. = 0031 hours ( 1231 hours – 1200 hours = 0031 hours)

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