Simple Time Difference

Lesson

When we want to find the difference between two numbers, we need to construct a subtraction number sentence and use any of the strategies you have learnt to solve it. For example, if we wanted to know the difference between $43$43 and $17$17, we could write this as: $43-17=26$43−17=26.

We can also find the difference between times in a similar way but it's important to remember that there are $60$60 minutes in an hour so we have to adjust our counting. People often forget this which can lead to errors. For example, the difference between $6$6 p.m. and $5:30$5:30 p.m. is $30$30 minutes. This is NOT the same as $6-5.3$6−5.3 which people commonly (and mistakenly) write as $0.7$0.7 or $70$70 minutes.

Remember!

$60$60 minutes makes $1$1 hour

Common time differences

1. Daylight savings time (DST)

Daylight savings time (DST) is used by lots of countries, including Australia, New Zealand, the USA and the UK during their summers. When Daylight Savings starts, everyone moves their clocks forward one hour. In other words, 9 am standard time would be 10 am DST.

This means that there is a 1 hour time difference between Standard Time and Daylight Savings Time.

2. Time Zones

The world is also split up into different time zones, which basically means the time will change depending on where you are in the world. If you have friends that live on the other side of the world, you'll know how important time differences are! For example, if you lived in Sydney, Australia and you called your friend in London at 12:30 pm DST (lunch time), it will actually be 1:30 am in London and they might get a bit cranky since you've probably woken them up!

Time Zones in Australia

Australia is divided into $3$3 time zones (shown in the map on the left). They are

Western Standard Time (WST), Central Standard Time (CST) and Eastern Standard Time (EST).

The time zones become a bit more tricky during Daylight Savings because not all the states use it. Queensland, the Northern Territory and Western Australia stay on Standard Time. The map on the right shows that during Daylight Savings, Australia actually has $5$5 time zones!

Examples

Question 1

If it is $8$8 $am$ in daylight savings time (DST), what time is it in standard time?

Question 2

Complete the table to show the time in each time zone.

WST	CST	EST
$\editable{}$$:$:$\editable{}$	$5$5$:$:$25$25	$\editable{}$$:$:$\editable{}$
$5$5$:$:$11$11	$\editable{}$$:$:$\editable{}$	$\editable{}$$:$:$\editable{}$
$\editable{}$$:$:$\editable{}$	$\editable{}$$:$:$\editable{}$	$12$12$:$:$25$25
$\editable{}$$:$:$\editable{}$	$7$7$:$:$17$17	$\editable{}$$:$:$\editable{}$