Finding the duration of time | Year 3 Mathematics PDF Download

What is duration?

Different terms used to discuss time include seconds, minutes, and hours.

• There are 60 seconds contained within each minute.
• Each hour comprises 60 minutes.

Duration refers to the length of time something lasts.

How to work out duration

• As the minute hand on a clock progresses from one numeral to the next, it signifies a passage of 5 minutes.
• A standard clock face features 12 numerals, each representing an interval of 5 minutes. Therefore, in one hour, there are 12 × 5 = 60 minutes.

Example

Example: Look at the two clocks to the right.
Can you say how much time has passed between the first and second one?
Sol: Count the intervals between the numbers in 5 minutes.
The clock on the left shows the time as five past seven. The clock on the right shows twenty-five past seven.
We can count 4 intervals of 5 minutes between the two times, so 4 x 5 = 20.
The duration of time that has passed is 20 minutes.

Spending time

There are alternative methods to efficiently calculate durations of time.

• In a quarter of an hour there are 15 minutes.
  
• In half an hour there are 30 minutes.
  
• In three quarters of an hour there are 45 minutes.

Using digital clocks

Calculating time durations using digital clocks is beneficial. For longer durations, we can think in terms of complete hours, half-hours, quarters, or three-quarters of an hour.

Example

Example: Can you work out the duration of time that has passed between these two digital clocks?
Sol: The digital clock on the left shows 06:45 or quarter to seven AM. The clock on the right shows 08:15 or quarter past eight AM.
There are different ways we could work this out, but a quick and efficient method is to add one hour to 06:45, to make 07:45, and then to add an extra half an hour, to bring the time to 08:15.
One hour = 60 minutes
Half an hour = 30 minutes
60 + 30 = 90 minutes
The duration of time that has passed is 90 minutes or one and a half hours.
When working out problems like this, we can think forwards or backwards in full hours, half hours, quarters or three quarters of an hour first, to get close to the answer, and then add or subtract intervals of 5 or fewer minutes to find the final answer.