The document discusses measurement of time in seconds (s) and the 24-hour clock. It provides examples of adding and subtracting times by following steps of adding or subtracting the hours and minutes separately, and adjusting if the minutes total 60 or more by subtracting 60 from the minutes and adding 1 to the hours. An example word problem is given about a family's travel times to solve for how long they stayed at the zoo, which was 6 hours and 30 minutes.

1. Measurement
Time
What will we learn today?
• measurement of time in seconds (s)
• 24-hour clock
• solving word problems involving time in
24-hour clock

2. Time is precious.
Time is a measurement.
We need to know the
techniques, so that we
can tell time accurately.

3. Adding and Subtracting Time
1. We need to Add or Subtract the hours and
minutes separately.
But you may need to do some adjusting if the
minutes end up 60 or more, or less than zero!
We will be discussing more on this in the later
slides.

4. Adding Times
Follow these simple steps:
1. Add the hours.
2. Add the minutes.
3. If the minutes are 60 or more, subtract 60
from the minutes and add 1 to hours.

5. Try this out!
1. This is an easy example:
What is 2:45 + 1:05?
Add the Hours: 2+1 = 3
Add the Minutes: 45+5 =50
The minutes have not exceeded 60,
so the answer is 3:50

6. Try this out!
2. This is a hard example:
What is 2:45 + 1:25 ?
Add the Hours: 2+1 = 3
Add the Minutes: 45+25 = 70
The minutes are 60 or more, so we have to
subtract 60 from minutes (70-60 = 10 Minutes)
and add 1 to Hours (3+1 = 4 Hours)
So, the answer is 4:10

7. Subtracting Times
Follow these simple steps:
1. Subtract the hours.
2. Subtract the minutes.
3. If the minutes are negative, add 60 to the
minutes and subtract 1 from hours.

8. Subtracting Times
1. This is an easy example:
What is 4:10 - 1:05 ?
Subtract the Hours: 4-1 = 3
Subtract the Minutes: 10-5 = 5
The minutes have not become negative ,
so the answer is 3:05

9. Subtracting Times
2. This is a hard example:
What is 4:10 - 1:25 ?
Subtract the Hours: 4-1 = 3
Subtract the Minutes: 10-25 = -15
The minutes are less than 0, so we have to
add 60 to Minutes
(-15+60 = 60-15 = 45 Minutes) and
subtract 1 from Hours (3-1 = 2 Hours)
So, the answer is 2:35

10. Try this out!
The Chan family set off for the zoo at 08 00.
They drove for 45 minutes and stopped for
breakfast at a coffee shop.
They ate for 1 h and it took them another
45 minutes to reach the zoo.
They left the zoo at 17 00.
How long did they stay
at the zoo?
Give your answers in hours and minutes.

11. Let’s do it step by step!
The Chan family set off for the zoo at 08 00.
0800

12. Let’s do it step by step!
The Chan family set off for the zoo at 08 00.
They drove for 45 minutes and stopped for
breakfast at a coffee shop.
0800 0845
45 minutes

13. Let’s do it step by step!
The Chan family set off for the zoo at 08 00.
They drove for 45 minutes and stopped for
breakfast at a coffee shop.
They ate for 1 h
0800 0845 0945
45 minutes 1 hour

14. Let’s do it step by step!
The Chan family set off for the zoo at 08 00.
They drove for 45 minutes and stopped for
breakfast at a coffee shop.
They ate for 1 h and it took them another
45 minutes to reach the zoo.
0800 0845 0945 1030
45 minutes 1 hour 45 minutes

15. Let’s do it step by step!
The Chan family set off for the zoo at 08 00.
They drove for 45 minutes and stopped for breakfast
at a coffee shop.
They ate for 1 h and it took them another
45 minutes to reach the zoo. They left the zoo at 17 00.
1030 1700
?
They reached the zoo at 1030.

16. How long did they stay at the zoo?
1030 1100 1200 1300 1400 1500 1600 1700
Let’s count backwards

17. How long did they stay at the zoo?
1030 1100 1200 1300 1400 1500 1600 1700
6 hours

18. How long did they stay at the zoo?
1030 1100 1200 1300 1400 1500 1600 1700
30 minutes
6 hours

19. How long did they stay at the zoo?
1030 1100 1200 1300 1400 1500 1600 1700
30 minutes
6 hours
6 hours 30 minutes

20. Are you ready to
try out the
questions?

21. Visit kungfumath.sg today!