## Converting speed

 Difficulty: Rating: GCSE Marks:

GCSE Text:
Whilst on holiday in Spain, Paddy’s hire car shows his speed in miles per hour, but the road signs are in km per hour.

He is driving in a ’20 km per hr’ zone, and his wife’s suggestion is to drive at 15mph which should keep him within the speed limit.

a) Explain why Paddy should not drive at 15mph. Show your workings and use Maths to justify your answer.

On the Spanish motorway, the signs show that the speed limit is 120 km per hour.

b) What speed in mph should you not exceed if you want to stay within the limit?

Suggestions:
Students are often intrigued by this video, as they consider travelling abroad in the future. It is expected that they know how to convert miles to km and back again, which often proves tricky with most classes. Once remembered, this is a straight forward yet practical problem that takes about 4 minutes to solve.

Extension Ideas:
Teachers could extend the learning by considering:

• The cost of hiring a car is €23 per day plus a mileage charge of 10 cents per mile. How much did it cost to hire the car for 9 days with a total of 350 miles travelled?