Time - a.m. and p.m., 12-hour and 24-hour Clock

# Time - a.m. and p.m., 12-hour and 24-hour Clock

## Time Facts

1 minute = 60 seconds
1 hour = 60 minutes
1 day = 24 hours
1 week = 7 days
1 year = 12 months
1 year = 365/366 days
1 year = 52 weeks
1 century = 100 years
1 millenium = 1000 years

## Clock Facts

1. The smaller hand is called the hour hand. It moves round the clock twice in 24 hours.
2. The bigger hand is called moves 24 times round the clock in 24 hours.
3. The face of the clock has 12 divisions.

## 12-hour Clock

A day consists of 24 hours. It starts from 12 midnight of one day and lasts till 12 midnight of the next day. In the 12-hour clock, the entire day is divided into two equal time zones of 12 hours each.

## A.M. and P.M.

We write a.m. to show morning time, before noon and after midnight.
a.m. stands for Ante-Meridiem, two Latin words meaning ‘Before Noon’.
We write p.m. to show afternoon or evening time, before midnight and afternoon.
p.m. stands for Post-Meridiem, two Latin words meaning, ‘After Noon’.
1. The time between 12 midnight to 12 noon is written as a.m.
2. The time between 12 noon to 12 midnight is written as p.m.

For example, 8 o’clock in the morning is written as 8 a.m. and 8 o’clock in the evening is written as 8 p.m.

## 24-hour Clock

In a 24-hour clock, the time is counted from 0 to 24. The time past 12 noon is expressed as 13, 14, 15, ..., 24.
1 p.m. is expressed as 13:00 hours, 2:30 p.m. as 14:30 hours, 5:30 p.m. is written as 17:30 hours and 8:15 p.m. is written as 20:15 hours.

We can represent 12-hour clock and 24-hour clock in the form of a circle. The time in 24-hour clock is marked on the outer side and the time in 12-hour clock is marked on the inner side of the circle. We need to add the term ‘hours’ after the time in 24-hour clock.
For example, 5 o’ clock in the evening is expressed as 5:00 p.m. in 12-hour clock and 17:00 hours in 24-hour clock.

## Converting 12-hour Clock Time into 24-hour Clock Time

i.                        If the time is in a.m., write the same time and put hours at the place of a.m.
ii.                        If the time is in p.m., add 12 to p.m. time and put hours at the place of p.m.

Example 1: Convert the following time in 24-hour clock time.

a.      7:00 a.m.
b.      9:00 p.m.
c.       10:30 a.m.
d.      11:45 p.m.

Solution: To convert 12-hour clock time, i.e., a.m. and p.m. into 24-hour clock, apply the rules given above.

a.      7:00 a.m. = 07:00 hours
b.      9:00 p.m. = (9:00 + 12) = 21:00 hours
c.       10:30 a.m. = 10:30 hours
d.      11:45 p.m. = (11:45 + 12) = 23:45 hours

## Converting 24-hour Clock Time into 12-hour Clock Time

i.                        If the time is less than 12:00 hours, write the same time and put a.m. at the place of hours.
ii.                        If the time is 13:00 hours or more, subtract 12 from hour time and put p.m. at the place of hours.
iii.                        If the time is between 12:00 hours and 13:00 hours, put p.m. at the place of hours.

Example 2: Convert the following time in 12-hour clock time.

a.      04:00 hours
b.      18:00 hours
c.       12:25 hours
d.      22:15 hours

Solution: To convert 24-hour clock time, into 12-hour clock, rules are as follows:

a.      04:00 hours = 4:00 a.m.
b.      18:00 hours = 18:00 – 12:00 = 6:00 p.m.
c.       12:25 hours = 12:25 p.m.
d.      22:15 hours = 22:15 – 12:00 = 10:15 p.m.

## Calculating Time Duration

To find the time duration of any event,
i.                    If the starting time and finishing time both are in a.m. or p.m., then directly subtract the starting time from the finishing time.
ii.                  If one of the starting time and finishing time are in a.m. and the other is in p.m., convert both the times in 24-hour clock time and then subtract the starting time from finishing time.

Example 3: Nidhi started for her office at 8:35 a.m. and reached at 9:45 a.m. How much time did she take to reach her office?

Solution: Since both the times are in a.m., we directly subtract the starting time from the reaching time.

Reaching time = 9:45 a.m.
Starting time = 8:35 a.m.
Time duration = 9:45 – 8:35 = 1:10

Thus, she took 1 hour 10 minutes to reach her office.

Example 4: An ODI match started at 9:30 a.m. and got over at 5:00 p.m. What was the total duration of the match?

Solution: Since the starting time is in a.m. and the finishing time is in p.m., we convert both the times in 24-hour clock time and then subtract.

Finishing time = 5:00 p.m. = 5:00 + 12:00 = 17:00 hours
Starting time = 9:30 a.m.  = 9:30 hours
Time duration = 17:00 – 9:30 = 7:30 hours

Thus, the total duration of the match was 7 hours 30 minutes.

## Calculating Number of Days

To calculate the number of days between two events, follow these steps:

Step 1: Make a table showing valid days in each month for the given period.
Step 2: Remove the starting day from the computation.
Step 3: Put all months before the ending month with number of days.
Step 4: Put all days of the ending month.
Step 5: Add and give the total.

Example 5: Rohit went to USA for some business work on 25th May 2019 and came back to his place on 11th September 2019. For how many days he was out from his place?

Solution: Find the number of days in each month. 25th May is not to be included and 11th September is to be included.

 Month Number of days May 6 June 30 July 31 August 31 September 11 Total 109

Thus, Rohit was out for 109 days from his own place.