How_To_Be_Good_At_Math

Calculating with time

Comparing time with

mixed units

Sometimes we’re asked to calculate

times that are in a mixture of units.

We need to be careful to make sure

the numbers are in the same unit

before we start calculating.

Look at the times of these

three flights from New

York. Let’s compare the

duration of each journey

and work out which is

the shortest flight.

It’s difficult to see which

is shortest when the time for

each journey is in a different unit.

Let’s convert them all into hours

to make it simpler to work out.

The flight to Buenos Aires is

already in hours, so we start

by converting the duration of the

flight to Dubai. There are 24

hours in a day, so we multiply

0.5 days by 24: 0.5 × 24 = 12.

So, the journey from New York to

Dubai takes 12 hours.

Next, we convert the time

taken for the Paris flight

into hours. We work this out

by dividing by 60, because

there are 60 minutes in an

hour: 480 ÷ 60 = 8. So, it takes

8 hours to fly from New York

to Paris.

We have worked out

that it takes 8 hours

to reach Paris, 11 hours to

reach Buenos Aires, and

12 hours to reach Dubai

from New York. So, the

journey to Paris is shortest.

Working with time

These robots are watching a

film that is two and a half

hours long. They have watched

80 minutes. How many

minutes of the film are left?

TRY IT OUT

Answer on page 319

New

York

Buenos

Aires

Dubai

Paris

New York to Paris

480 minutes

New York

to Dubai

0.5 days

New York to

Buenos Aires

11 hours

THE END

First, convert the length

of the film into minutes.

Now all you need to do

is subtract the number

of minutes watched from the

total length of the film.

196-197_Calculating_with_time.indd 197 29/02/2016 18:04