We have always been interested in keeping track of time. Sundials were the first way used to keep of track of time. The sundial had limits. It needed the sun and could not keep track of time at night. Through the centuries, many things have been used to keep track of time. In our modern society, we have used clocks. There are two types of clocks; digital and analog. Digital clocks display the time as numbers.

Analog clocks are clocks with hands. The shorter hand tells the hour and the longer hand tells the minutes. An easy way to remember the hour hand and the minutes hand is that hour is a shorter word than minute, and the shorter hand tells the hour.

In an analog clock, the minute hand travels faster than the hour hand as it has to cover 60 minutes. The hour hand only needs to travel between the numerals in the same time it takes the minute hand to cover 60 minutes.

To tell what time it is, look at the shorter hand to figure out what hour it is. Next, look at the minute hand to figure out the minutes. Each numeral of the clock represents a certain number of minutes. Look at the chart.

24-hour Clock

Your friend said she would meet you at 8:00 o’clock. Does that mean in the morning or the evening? We use a.m. and p.m. to know whether it is morning or evening.

Another way to avoid confusion is by using the 24-hour clock. Airlines, military and health care are examples of places where the 24-hour clock is used.

With the 12-hour clock, each of the hours is repeated is a day. In the 24-hour clock, each hour in a day is counted giving us 24 hours. In the 24-hour clock, 12:00 a.m. can be written as 0000 or 2400. 0000 is the start of a new day, while 2400 is the end of the day.

We write times with 4 digits. The first two digits are the hours and the next two digits are the minutes.

For example, 8:20 a.m. would be 0820, while 8:20 p.m. would be 2020.

To convert 12-hour clock to 24-hour clock, add 12 to the hour for any times after 1:00 p.m. to 11:59 p.m.

Example: 6:30 p.m.

6:30 + 12:00 = 1830

Example: 10:30 p.m.

10:30 + 12:00 = 2230

When writing times in 24-hour clock, we do not use a colon.

Topic C: Self-Test

Mark    /22    Aim 17/22

1. Write the time shown on each clock. (6 marks)
   1. 
   2. 
   3. 
   4. 
   5. 
   6. 
2. Under each clock is a time on a digital clock. Put the hands on the analog clock to show the digital time. (4 marks)
   1. 
   2. 
   3. 
   4. 
3. Change each 12-hour clock time to 24-hour clock time. Watch carefully for a.m. and p.m. (6 marks)
   1. 6:25 a.m.
   2. 11:05 p.m.
   3. 2:55 p.m.
   4. 10:40 a.m.
   5. 4:00 p.m.
   6. 8:15 a.m.
4. Change each 24-hour clock time to 12-hour clock time. Watch carefully for a.m. and p.m. (6 marks)
   1. 0155
   2. 0020
   3. 1935
   4. 0545
   5. 1530
   6. 2110

Answers to Topic C Self-Test

1. 1. 12:35
   2. 4:15
   3. 2:10
   4. 10:53
   5. 7:22
   6. 9:44
2. 1. 
   2. 
   3. 
   4. 
3. 1. 0625
   2. 2305
   3. 1455
   4. 1040
   5. 1600
   6. 0815
4. 1. 1:55 a.m.
   2. 12:20 a.m.
   3. 7:35 p.m.
   4. 5:45 a.m.
   5. 3:30 p.m.
   6. 9:10 p.m.