• measurement of time in seconds (s)

• 24-hour clock

• solving word problems involving time in 24-hour clock

What will we learn today?

Measurement Time

Time is precious. Time is a measurement.

We need to know the techniques, so that we

can tell time accurately.

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.

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.

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

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

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.

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

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

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.

Let’s do it step by step!

The Chan family set off for the zoo at 08 00.

0800

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

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

45 minutes

0945

1 hour

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

45 minutes

0945

1 hour 45 minutes

1030

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

They reached the zoo at 1030.

1700

?

How long did they stay at the zoo?

1030 1700

Let’s count backwards

1600 1500 1400 1300 1200 1100

How long did they stay at the zoo?

1030 1700 1600 1500 1400 1300 1200 1100

6 hours

How long did they stay at the zoo?

1030 1700 1600 1500 1400 1300 1200 1100

6 hours

30 minutes

How long did they stay at the zoo?

1030 1700 1600 1500 1400 1300 1200 1100

6 hours

30 minutes

6 hours 30 minutes

Are you ready to try out the questions?

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