 Study P4 Mathematics Maths - Time - Geniebook   # Time

In this article, we will be learning about the conversion of time and the 24-hour clock. The lesson objectives are:

1. Conversion of time
2. 24-h clock

## Topic Recap:

### Conversion of Time

We can express time in hours and minutes to minutes.

Examples:

1. $$1 \text{ h } = 60 \text{ min}$$
2. \begin{align}\\ 2 \text{ h } &= 2 \times 60 \text{ min}\\ &= 120 \text{ min} \end{align}
1. \begin{align}\\ 3 \text{ h } 20 \text{ min } &= 180 \text{ min }+ 20 \text{ min }\\ &= 200 \text{ min } \end{align}

We can also express time in minutes to hours and minutes.

Examples:

1. $$180 \text{ min } = 3 \text{ h } 0 \text{ min }$$
2. \begin{align}\\ 400 \text{ min } &= 360 \text{ min }+ 40 \text{ min }\\ &= 6 \text{ h } 40 \text{ min } \end{align}

## 1. Conversion Of Time

$$1 \text{ minute } = 60 \text{ seconds}$$

To express time from minutes to seconds, we multiply the number of minutes by 60.

To express time from seconds to minutes, we divide the number of seconds by 60.

$$1 \text{ hour} = 60 \text{ minutes}$$

To express from hours to minutes, we multiply the number of hours by 60.

To express from minutes to hours, we divide the number of minutes by 60.

Question 1:

Express the following time in seconds.

1. 2 min = __________ s
2. 2 h = __________ s
3. $$\frac {1}{4}$$ h = __________ s

Solution:

1. \begin{align}\\ 2 \text{ min } &= 2 \times 60\\ &= 120 \text{ s} \end{align}

120 s

1. \begin{align}\\[2ex] 2 \text{ h } &= 2 \times 60\\ &= 120 \times 60\\ &= 7200 \text{ s} \end{align}

7200 s

1.  $$\frac {1}{4} \text{ h}$$

1 h = 60 min

$$\frac {1}{4}$$h   = 60 min ÷ 4

= 15 min

15 min = 15 60 s

15    = 900 s

900 s

Question 2:

Express the following time in seconds.

5 min = __________ s

Solution:

5 min = 5 × 60 s

= 300 s

300 s

Question 3:

Express the following time in seconds.

45 min = __________ s

Solution:

45 min = 45 × 60 s

= 45 × 6 × 10

= 2700 s

2700 s

Question 4:

Express the following time in seconds.

$$1\frac {1}{2}$$ h = __________ s

Solution:

1 h = 3600 s

$$\frac {1}{2}$$= 30 min

= 30 × 60

= 1800 s

$$1\frac {1}{2}$$= 3600 s + 1800 s

= 5400 s

5400 s

Question 5:

Express the following time in minutes or hours and minutes.

1. 180 s = __________ min
2. 3000 s = __________ min
3. 4500 s = __________ h __________ min

Solution:

1. 180 s = 180 ÷ 60

= 3 min

3 min

1. 3000 s = 3000 ÷ 60

= 50 min

50 min

1. 4500 s = 4500 ÷ 60

= 75 min

= 1 h 15 min

OR

1 h = 3600s

4500 s - 3600 s = 900 s

= 900 ÷ 60

= 15 min

Hence, 4500 s = 1 h 15 min

1 h 15 min

Question 6:

Express the following time in minutes or hours and minutes.

120 s = __________ min

Solution:

120 s

= 120 ÷ 60

= 2 min

2 min

Question 7:

Express the following time in minutes or hours and minutes.

300 s = ___________ min

Solution:

300 s

= 300 ÷ 60

= 5 min

5 min

2) 24-h clock

In the 24-hour clock, there is no need to add suffixes like am or pm. It is written in 4 digits, where the first two digits represent the hour and the last two digits represent the minutes.

Time from midnight to noon:

12-h clock = 12:00 am to 11:59 am

24-h clock = 00 00 to 11 59

Time from noon to midnight:

12-h clock = 12:00 pm to 11:59 pm

24-h clock = 12 00 to 23 59

Example:

 12-h clock 24-h clock 5:30 am 05:30 5:30 pm 17:30 10:30 am 10:30 10:30 pm 22:30 12:00 pm 12:00 12:00 am 00:00

Question 1:

Express the following time in 24-hour clock.

1. 8:50 am = __________
2. 12:20 am = __________
3. 9:10 pm = __________

Solution:

a) 8:50 am = 08 50

08 50

b) 12:20 am = 00 20

00 20

c) 9:10 pm = 21 10

21 10

Question 2:

Express the following time in 24-hour clock.

2:35 am = __________

Solution:

2:35 am = 02 35

Question 3:

Express the following time in 24-hour clock.

11:15 pm = __________

Solution:

11:15 pm = 23 15

23 15

Question 4:

Which of the following clocks shows the time 19:15? Solution:

19 15 is 7:15 pm in the evening.

(4)

Question 5:

Express the following time in 12-hour clock.

1. 03 30 = __________
2. 12 50 = __________
3. 17 45 = __________

Solution:

1.  03 30 = 3:30 am

1. 12 50 = 12:50 pm

1. 17 45 = 5:45 pm

Question 6:

Express the following time in 12-hour clock.

00 10 = __________

Solution:

00 10 = 12:10 am

12:10 am

Question 7:

Express the following time in 12-hour clock.

20 15 = __________

Solution:

20 15 = 8:15 pm

8:15 pm

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