Cambridge International Mathematics

Topics in arithmetic (Chapter 10) 225

Example 23 Self Tutor

Biathlete Jo cycles 60 km at a speed of 30 km/h, and then runs another 15 km at a speed

of 10 km/h. Find:

a the total time b the average speed for Jo’s training session.

a

b

EXERCISE 10G

1 An Olympic sprinter runs 100 min 10 : 05 seconds. Calculate his average speed in:

a m/s b km/h

2 A car travels for 2 h 20 min at an average speed of 65 km/h. Calculate the distance travelled.

3 How long does it take, in seconds, for a 160 m long train to enter a tunnel when the train is travelling

at 170 km/h?

4 Jane can run 11 : 4 km in 49 min 37 sec. Calculate her average speed in km/h.

5 Find the time taken, to the nearest second, to:

a drive 280 km at an average speed of 95 km/h

b run10 000m at an average speed of 11 km/h.

6 Find the distance travelled when:

a walking at an average speed of 3 : 5 km/h for 2 h 15 min

b flying at an average speed of 840 km/h for 6 h 35 min.

7 A student walks for 2 hours at 3 : 5 km/h and then for 1 hour at 2 km/h. Find:

a the total distance walked b the average speed.

8 In a 42 : 2 km marathon, Kuan runs the first 35 km at an average speed of 11 km/h. He walks the

next 6 km at 4 : 5 km/h, and staggers the final 1 : 2 km at 1 : 5 km/h. Find Kuan’s average speed for the

marathon.

9 A family drives 775 km for their holiday. The first part of the trip is 52 km and takes 1 h 10 min. The

remainder is covered at an average speed of 100 km/h. Find the average speed for the whole journey.

10 Convert: a 15 m/s into km/h b 120 km/h into m/s.

1 st leg: t=

d

s

=

60 km

30 km/h

=2hours

2 nd leg: t=

d

s

=

15 km

10 km/h

=1: 5 hours

) total time=2hours+1: 5 hours=3: 5 hours

Total distance travelled=60km+15km=75km

) average speed s=

d

t

=

75 km

3 : 5 h

¼ 21 : 4 km/h

IGCSE01

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Y:\HAESE\IGCSE01\IG01_10\225IGCSE01_10.CDR Friday, 14 November 2008 12:12:16 PM PETER