# Use Time Calculations

In this worksheet, students will practise counting forwards to calculate end times, backwards to calculate start times or find the difference between two times using calculations based around 60.

Key stage:  KS 4

GCSE Subjects:   Maths

GCSE Boards:   AQA, Eduqas, Pearson Edexcel, OCR

Curriculum topic:   Ratio, Proportion and Rates of Change, Mensuration

Curriculum subtopic:   Ratio, Proportion and Rates of Change, Units and Measurement

Difficulty level:

### QUESTION 1 of 10

Time calculations are based around the number 60.

Remember, there are 60 minutes in an hour and 60 seconds in a minute.

When dealing with calculations involving time, the most common mistake to make is to try and use 'normal' addition and subtraction.

Normal calculation is based around regular place value i.e. 10, 100, etc.

The easiest and most reliable way to calculate time is by counting on to the next hour.

Let's look at this method in action using some examples now.

e.g. A TV programme starts at 09:00 and lasts 75 minutes. What time does it finish?

If we start at 09:00 and add 60 minutes, we reach 10:00.

This leaves us with 15 minutes until the programme ends, which will be at 10:15.

As this programme started on the hour exactly, it was easier to calculate its end time.

Let's work through another example now where we must work backwards.

e.g. A 50-minute tv show ends at 15:45. What time did it start?

For this one, we're going backwards so we need to count down.

From 15:45 to 15:00, we have used 45 minutes.

We just need to take an extra 5 minutes off.

This means the programme must have started at 14:55.

e.g. The winner of a formula one race has a finishing time of 1 hr 58 minutes. If the second-place finisher has a time of 2 hrs 4 minutes, how long after the winner did the 2nd place driver finish?

This is easier than it looks, as all we want to know is the difference between 1 hr 58 mins and 2 hrs 4 mins.

If we count on to the next full hour from 1 hr 58 mins, it takes 2 minutes to reach 2 hours.

We can then add 4 minutes more to arrive at 2 hrs 4 minutes.

This means that the total difference between the two times is 6 minutes.

In this activity, we will count forwards to calculate end times, backwards to calculate start times or find the difference between two times, all using calculations based around the number 60.

Write a word or number in the space to complete the sentence below.

A TV programme starts at 17:15 and finishes at 17:50.

How long is the programme?

25 minutes

35 minutes

45 minutes

Joel puts a chicken in the oven at 16:10.

It takes 1 hr and 45 minutes to cook.

What time does Joel take the chicken out of the oven?

Give your answer as a time in the format HH:MM with no spaces and using the colon key (:) between the hours and minutes.

Match each programme start time and length on the left with their correct end time on the right.

## Column B

Start: 09:00; Length: 50 mins
End: 14:15
Start: 16:00; Length: 70 mins
End: 17:10
Start: 12:30; Length: 1 hr 45 mins
End: 09:50

A film at the cinema ends at 16:40.

If it was 25 minutes long, what time did it start?

16:25

16:15

16:65

Samira is baking some jacket potatoes for dinner.

They take 1 hr and 15 minutes to cook and she wants to eat them at 18:00.

What time does Samira need to start cooking?

Give your answer as a time in the format HH:MM with no spaces and using the colon key (:) between the hours and minutes.

Match each programme end time and length on the left with their correct start time on the right.

## Column B

End: 09:00; Length 50 mins
Start: 10:45
End: 16:00; Length 70 mins
Start: 08:10
End 12:30; Length 1 hr 45 mins
Start: 14:50

A dance class starts at 16:20 and ends at 16:44.

How long is the class?

28 minutes

24 minutes

0.24 hours

Roy put his slow cooker on at 08:45 and turned it off at midday.

How long was it on for?

28 minutes

24 minutes

0.24 hours

Match each programme start and end time on the left with their correct length on the right.

## Column B

Start: 14:45; End: 16:15
1.5 hours
Start 07:30; End 07:45
0.5 hours
Start 13:40; End 14:10
0.25 hours
• Question 1

Write a word or number in the space to complete the sentence below.

EDDIE SAYS
The most essential fact to keep in mind when calculating with times is that 60 is the most important number. This is because there are 60 seconds in a minute, and 60 minutes in an hour. Keep this fact at the front of your mind during the rest of this activity.
• Question 2

A TV programme starts at 17:15 and finishes at 17:50.

How long is the programme?

35 minutes
EDDIE SAYS
As both of these times are related to 5 pm (17:00), we don't need to worry about going over the hour mark. Therefore, we can just subtract 15 from 50 to find the length of the programme: 50 - 15 = 35 minutes
• Question 3

Joel puts a chicken in the oven at 16:10.

It takes 1 hr and 45 minutes to cook.

What time does Joel take the chicken out of the oven?

Give your answer as a time in the format HH:MM with no spaces and using the colon key (:) between the hours and minutes.

17:55
EDDIE SAYS
This is easier to split into the two elements - add the hour first and then the 45 minutes. If we add an hour to 16:10, we reach 17:10. If we then add a further 45 minutes, we reach 17.55. Did you type that answer in correctly using the format described in the question?
• Question 4

Match each programme start time and length on the left with their correct end time on the right.

## Column B

Start: 09:00; Length: 50 mins
End: 09:50
Start: 16:00; Length: 70 mins
End: 17:10
Start: 12:30; Length: 1 hr 45 min...
End: 14:15
EDDIE SAYS
Let's begin with each start time and add on the specified length, to find the correct end time in each case. If we start at 9:00 and add 50 minutes, we reach 9:50 - simple! Let's split the '70 minutes' length in the second option into 60 + 10 to make our life easier. 16:00 + 60 minutes (or 1 hour) = 17:00 17:00 + 10 minutes = 17:10 If we add an hour to 12:30 first, we reach 13:30. Then let's split the remaining 45 minutes into 30 + 15. 13:30 + 30 minutes = 14:00 14:00 + 15 minutes = 14:15 How did you get on with matching those?
• Question 5

A film at the cinema ends at 16:40.

If it was 25 minutes long, what time did it start?

16:15
EDDIE SAYS
Did you notice that the length given was less than the minutes shown in the time? This means that we won't go past an hour and we can simply subtract the two numbers as usual: 40 - 25 = 15 So the start time of the film was 16:15.
• Question 6

Samira is baking some jacket potatoes for dinner.

They take 1 hr and 15 minutes to cook and she wants to eat them at 18:00.

What time does Samira need to start cooking?

Give your answer as a time in the format HH:MM with no spaces and using the colon key (:) between the hours and minutes.

16:45
EDDIE SAYS
Splitting up the 1 hr and 15 minutes into easier chunks is the key to success in this question. Working backwards from 18:00, we should first subtract the full hour and then we just need to take away a further 15 minutes: 18:00 - 1 hour = 17:00 17:00 - 15 minutes = 16:45 Did you input that time correctly in the specified format?
• Question 7

Match each programme end time and length on the left with their correct start time on the right.

## Column B

End: 09:00; Length 50 mins
Start: 08:10
End: 16:00; Length 70 mins
Start: 14:50
End 12:30; Length 1 hr 45 mins
Start: 10:45
EDDIE SAYS
Let's begin with each end time and take away the specified length, to find the correct start time in each case. If we end at 9:00 and subtract 50 minutes, we reach 8:10 - off to a good start! Let's split the '70 minutes' length in the second option into 60 + 10 to make our life easier. 16:00 - 60 minutes (or 1 hour) = 15:00 15:00 - 10 minutes = 14:50 If we subtract an hour from 12:30 first, we reach 11:30. Then let's split the remaining 45 minutes into 30 + 15. 11:30 - 30 minutes = 11:00 11:00 - 15 minutes = 10:45 How did you get on with matching those?
• Question 8

A dance class starts at 16:20 and ends at 16:44.

How long is the class?

24 minutes
EDDIE SAYS
Remember that for time calculations, we cannot use normal methods, we must use the counting on / back method. As both of these times are related to 4pm (16:00), we can simply subtract the minutes: 16:44 - 16:20 = 24 minutes
• Question 9

Roy put his slow cooker on at 08:45 and turned it off at midday.

How long was it on for?

EDDIE SAYS
Remember that the word 'midday' simply means 12:00. If we count forwards from 08:45 to the next hour, we need to add 15 minutes to reach 09:00. Between 09:00 and 12:00, there are 3 hours. 3 hours + 15 minutes = 3 hours and 15 minutes
• Question 10

Match each programme start and end time on the left with their correct length on the right.

## Column B

Start: 14:45; End: 16:15
1.5 hours
Start 07:30; End 07:45
0.25 hours
Start 13:40; End 14:10
0.5 hours
EDDIE SAYS
One of the things which examiners love to do is to tie together topics. In this case, we have tied together time and decimals. We can choose to begin with each start time and count on to the end time, or vice versa. If we start at 14:45, we need to add 15 mins to reach 15:00, then 1 hour to reach 16:00, and finally 15 mins to reach 16:15. 60 + 15 + 15 = 90 mins But how do we express this as a decimal? One hour is 60 minutes as we know, so 90 minutes is the same as 1 hour and a half or 1.5. If we work backwards from 07:45, we need to subtract 15 minutes to reach 07:30. 15 minutes = a quarter of an hour or 0.25 If we start at 13:40, we need to add 20 mins to 14:00, then 10 mins to reach 14:10. 20 + 10 = 30 30 mins = half an hour or 0.5 You've completed this activity, and can now find start and end times, plus duration, using the methods of counting on or back from 60.
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