Page 159 - ICSE Math 4

4. Write the me for the following.
(a) 4 hours before 10:20 a.m. (b) 3 hours a er 9:45 a.m.

(c) 15 minutes a er 12 midnight (d) 45 minutes before 12 noon
(e) 8 hours 20 minutes a er 4:10 a.m. (f) 2 hours 15 minutes before 7:35 p.m.

5. Express the following as a.m. or p.m. according to your rou ne.

(a) Breakfast me (b) Lunch me (c) Play me (d) Dinner me
(e) Wake up me in the morning (f) Sleeping me at night

24-Hour Clock
24
23 13
We know that railway sta ons, airports 12
22 11 1 14
and hospitals do not use 12-hour clock 10 2
21 9 3 15
to express me in a.m. and p.m. Instead,
8 4
they use a 24-hour clock that runs from 20 7 6 5 16
19 17
midnight to midnight and is divided into 24 18
hours. Look at the given 24-hour clocks. Analog clock Digital clock

The format of me in a 24-hour clock is hours : minutes or hours : minutes : seconds. This
format is also used in computers and digital watches.

Conversion of 24-Hour Clock Time to 12-Hour Clock Time

• If the given me is between 0000 hours and 0059 hours, add 1200 hours and a.m.
to it.

For example, 0045 hours = 0045 hours + 1200 hours = 1245 hours = 12:45 a.m.
• If the given me is between 0100 hours and 1159 hours, just add a.m. to it.

For example, 1140 hours = 11:40 a.m. and 0950 hours = 09:50 a.m.

• If the given me is between 1200 hours and 1259 hours, just add p.m. to it.
For example, 1230 hours = 12:30 p.m. and 1255 hours = 12:55 p.m.

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

For example, 2305 hours = 2305 hours – 1200 hours = 1105 hours = 11:05 p.m.

Conversion of 12-Hour Clock Time to 24-Hour Clock Time

• If the given me is between 12:00 midnight and 12:59 a.m., subtract 12 hours (12:00)
from it.

For example, 12:45 a.m. = 1245 hours – 1200 hours = 0045 hours or 00:45
• If the given me is between 1:00 a.m. and 12:59 p.m., write it as it is.

For example, 10:50 a.m. = 1050 hours or 10:50

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