Topics
9. 2D Measurement
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AustraliaNSW
Stage 3

9.07 Time

Lesson
Practice
Lesson

Are you ready?

Can you  convert units of time? 

Examples

Example 1

It takes around 300 minutes to drive from Sydney to Thredbo. How many hours is this?

Worked Solution
Create a strategy

Divide the number of minutes by the number of minutes in an hour.

Apply the idea

1\text{ hour} = 60\text{ minutes}, so we need to divide by 60.

\displaystyle 300 \div 60\displaystyle =\displaystyle \dfrac{300}{60}Write as a fraction
\displaystyle =\displaystyle \dfrac{30}{6}Cancel out the zeros
\displaystyle =\displaystyle 5Divide 30 by 6

The drive takes 5 hours.

Idea summary

Remember:

\begin{aligned} 1\text{ Week} &= 7\text{ Days}\\ 1\text{ Day} &= 24\text{ Hours}\\ 1\text{ Hour} &= 60\text{ Minutes}\end{aligned}

Passing time

This video looks at calculating passing time in minutes and hours and seconds.

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Examples

Example 2

Find the value of 5 hours 10 minutes - \, 2 hours 40 minutes.

Worked Solution
Create a strategy

Use a vertical algorithm and the conversion 1 \text{ hour}= 60 \text{ minutes}.

Apply the idea

To subtract the times, we can write it in a vertical algorithm. Make sure to align the hours, colon and minutes.\begin{array}{c} & &5 & : &10 \\ &- &2 & : & 40 \\ \hline & \\ \hline \end{array}

Since 10 minutes is less than 40 minutes, we trade 60 minutes from 5 hours.

So, we have 10+60=70 minutes in the first row and 5 hours becomes 4 hours.\begin{array}{c} & &4 & : &70 \\ &- &2 & : & 40 \\ \hline & \\ \hline \end{array}

Subtracting each column, we have:\begin{array}{c} & &4 & : &70 \\ &- &2 & : & 40 \\ \hline & &2&:&30 \\ \hline \end{array}

The difference is 2 hours and 30 minutes.

Idea summary

We can use subtraction to find the difference between times, but we have to be careful when we need to regroup and remember:

\displaystyle 1 \text{ hour}\displaystyle =\displaystyle 60 \text{ minutes}
\displaystyle 1 \text{ minute}\displaystyle =\displaystyle 60 \text{ seconds}

Time

This video looks at days, weeks and years.

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Examples

Example 3

Answer the questions below to find the number of hours in 6 months. You may assume there are 30 days in a month.

a

Convert 6 months into days.

Worked Solution
Create a strategy

We can assume that there are 30 days in a month. So we need to find 6 lots of 30 days.

Apply the idea
\displaystyle 6 \text{ months}\displaystyle =\displaystyle 6 \times 30 \text{ days}Multiply 30 by 6
\displaystyle =\displaystyle 180 \text{ days}
b

Convert 180 days into hours.

Worked Solution
Create a strategy

There are 24 hours in a day, so we multiply the number of days by 24.

Apply the idea
\displaystyle 180 \text{ days}\displaystyle =\displaystyle 180 \times 24 \text{ hours}Multiply by 24
\displaystyle =\displaystyle 4320 \text{ hours}Use your calculator
Idea summary

  • There are 60 seconds in 1 minute.

  • There are 60 minutes in 1 hour.

  • There are 24 hours in 1 day.

  • There are 365 days in 1 year.

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