We normally use 12-hour clock system. The hour hand of the clock goes round the dial twice a day (24 hours). Some departments like railways, Airlines, etc use 24-hour clock system because they do not use a.m. and p.m. times.

In a 24-hour clock system, we express time in four digits. The first
two digits represent hours and the last two digits represent the
minutes.

On the dial there are two concentric circles. The inner circle has 1 to 12 numbers while the outer circle has 13 to 24 numbers.

In a 24-hour clock system, we start counting the time from midnight. Let us understand 24-hour system by considering some examples.

(i) 12 midnight is denoted by 24 00 hours or 00 00 hour.

(ii) 12 noon is denoted by 12 00 hours.

(iii) 6 in the morning is denoted by 06 00 hours.

(iv) 10:25 in the evening is denoted by 22 25 hours.

(10:25 + 12:00)

(v) 7:15 in the evening is denoted by 19 15 hours.

(7:15 + 12:00)

From the above examples, we can conclude that between 12 midnight and 12 noon the 24-hour clock time is same.

For example, 10 40 hours = 10:40 a.m., 08 20 hours = 8:20 a.m., 11 30 hours = 11:30 a.m.

But between 12 noon and 12 midnight to convert the 24-hour clock time into 12-hour clock time, we subtract 12 from the 24-hour time.

For example, 19:30 hours = 19:30 – 12:00 = 7:30 p.m.

Similarly, to convert the 12-hour clock time into 24-hour clock time between 12 noon and 12 midnight, we add 12.

For example, 11:30 p.m. = 11:30 + 12:00 = 23:30 hours.

Therefore, the time which is shown by the inner circle is the time before noon and that shown by the outer circle is the time after noon.

**These are some more examples:**

*After midnight* 00:10 a.m. is shown as 00:10

02:45 a.m. is shown as 02:45

10:48 a.m. is shown as 10:48

02:45 p.m. is shown as 14:45

10:48 p.m. is shown as 22:48

** Clock General Time 24 hour clock**

00:00 midnight 00:00

(Just after midnight) (Just after

or, midnight) or,

12:00 midnight 24:00 hours

06:00 a.m.(6 hours 06:00

zero minutes

in the morning)

12:00 noon 12:00

06:10 p.m. 18:10

08:30 p.m. 20:30

10:45 p.m. 22:45

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**4th Grade Math Activities**

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