We know that, the world is going fast with the time and our every work is time dependent. In our daily life the time we see or understand is the time of 12 hours clock. But, at railway station the clock used or considered is 24 hours clock to avoid the confusion of travelers. But, in both the clock system hour, minute and second relation is the same.

That means, 1 hour = 60 minutes

1 minute = 60 seconds

- In both 12 hour and 24 hour clock, when hour hand completes one rotation means 12 hours.
- If minute hand completes one rotation then it means 60 minutes i.e. 1 hour.
- If second hand completes one rotation then it means 60 seconds or 1 minute.

- In above fig, there is a 12 hour clock, in which hour hand is on 5 and minute hand is on 3. Hence, the time is 5:15, but it may be a.m. or p.m.
- If it is 5:15 a.m. that means morning time and it represents 5 hours 15 minutes.
- If it is 5:15 p.m. that means evening time and it also represent 5 hours 15 minutes.

- The above figure shows the 12 hour clock time notation, in which hour hand is on 3 and minute hand is on 8. But here not mentioned clearly that a.m. or p.m.
- If it is 3:40 a.m. that means morning timing and it represents 3 hours 40 minutes.
- If it is 3:40 p.m. that means noon timing and it also represents 3 hours 40 minutes.

The following figure 1 shows the 12 hours clock and the second clock shows the 24 hours clock.

**Fig. 1) 12 Hour Clock**

**Fig. 2) 24 Hour Clock**

The difference between them is, in 12 hours clock time is expressed by considering 12 hours only. While in 24 hours clock time is expressed by considering 24 hours as shown in figure.

To understand the 12 hour clock and 24 hour clock without confusion we learn it through the number line format as given below.

- The numbers above the number line are from 0 to 24 which shows 24 hour clock. And the numbers below number line are from 0 to 12 only, hence shows 12 hour clock.
- And we see that, how 12 hour clock time corresponds to 24 hour clock time and vice versa.
- In 12 hour clock, the time from 0 to 12 is represented by a.m., and after again 12 it starts from 1 then it is represented as p.m. up to again 12.
- In short, we use a.m. to represent the time from 12 midnight to 12 noon. And p.m. represents the time from 12 noon till the 12 in the mid night.
- And main thing which we have to remember is the 24 hours clock doesn’t uses a.m. or p.m. to represent the time as shown in figure.

**Conversion of 12 hours clock time into 24 hour clock time:**

- While converting the 12 hour clock time into the 24 hour clock time, if a.m. is given then we take the time as it is without writing a.m.
- And if time is given in p.m. then to convert it into 24 hour clock time we add 12 hours.
- To understand more clearly see the following examples.

**For example:**

1) 3:00 p.m.

Here, p.m. is given hence we add 12 and write it as,

3:00 + 12:00 = 15:00

Thus, in 24 hour clock 3:00 p.m. means 15:00

2) 6:00p.m.

Here also p.m. is given and hence to convert it into 24 hour time we add 12 and write

as,

6:00 p.m. = 6:00 p.m. + 12:00 = 18:00

Thus, in 24 hour clock 6:00 p.m. means 18:00.

3) 8:00 a.m.

Now, here a.m. is given that means it is morning time and hence we can’t add 12 here

and write it as same.

In 24 hour clock 8:00 a.m. means 8:00 only.

4) 11:30 a.m.

Here a.m. is given and hence we can’t add 12. Thus, 11:30 a.m. in 24 hour clock is represented as,

11:300 a.m. = 11:30 only.

5) 4:25 p.m.

Here, p.m. is given hence we add 12 and write it in 24 hour clock time as,

4:25 + 12 = 16:25

Here, 4 and 12 represents hours and 25 represents minutes.

Thus, 4:25 p.m. in 24 hour clock is expressed as 16:25.

**Conversion of 24 hour clock time into 12 hour clock time:**

- While converting time from 24 hour clock to 12 hour clock, if time is given below 12 hours, then we have to write it as it is with a.m.
- And if time is given above 12 hours, then we have to subtract 12 from it and have to write p.m.
- To understand more clearly see the following examples.

**For example:**

1) 17:20

Here given that 17 hours 20minutes that is the time is above 12 hours. Hence, we subtract 12and write as,

17:20 – 12:00 = 5:20 p.m.

Thus, 17:20 means 5:20 p.m. in 12 hour clock.

2) 8:30

Here the time is given below 12 hours, hence we write it as it is with a.m.

Hence, 8:30 = 8:30 a.m. in 12 hour clock

3) 23:30

Here time is given above 12 hours, hence we subtract 12 from it and write it as p.m.

23:30 means 23:30 – 12:00 = 11:30 p.m. in 12 hour clock time.

4) 3:00

Here the time is given below 12 hours, hence we write as it is with a.m.

Hence, 3:00 in 12 hour clock is 3:00 a.m.