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4.3 Using compound measures

6 A 500 g bag of rice costs $0.64. A 2 kg bag of the same rice costs $2.65.
Which bag is better value for money?
7 A 330 ml bottle of mineral water costs $0.42. A 1.5 litre bottle of the same water costs $1.65.
Which bottle is better value for money?
1
8 Marc likes to solve number puzzles. It took him 4 minutes to complete one puzzle with
2
18 numbers.
It took him 6 minutes 24 seconds to complete a different puzzle with 32 numbers.
a For each puzzle work out how many seconds it took Marc to complete one number.
b Use your answer to part a to decide which puzzle Marc completed faster.

9 Ricardo goes on holiday by car. The travel graph
shows his car journey. He stopped once for a break. 500
a Work out Ricardo’s average speed for: 400
i the first part of the journey, before he took a break 300
ii the second part of the journey, after he took a break. Distance (km) 200
b During which part of the journey was Ricardo
travelling faster? 100
c Work out Ricardo’s average speed for the whole 0
journey, including the break. 0 1 2 3 4 5 6 7
Time (hours)

10 Lauren cycled to visit her Aunt. The travel graph shows
her journey to and from her Aunt’s house. 25
1
She stayed with her Aunt for 1 hours before
3
returning home. 20
a Work out Lauren’s average speed for: Distance (km) 15
i the journey to her Aunt’s house
ii the journey home from her Aunt’s house. 10
b During which part of the journey was 5
Lauren travelling fastest? 0
c Work out Lauren’s average speed for the 0 1 2 3
whole journey. Time (hours)
Do not include the time she spent at her Aunt’s house.

Summary

You should now know that: You should be able to:
+ When you solve problems you should write down + Solve problems with measurements in a variety of
every step in your working, check your working is contexts.
correct and check your answers are reasonable. + Solve problems involving average speed.
+ The three formulae linking distance, speed and + Use compound measures to make comparisons in
time are: c distance = speed × time real-life contexts, such as travel graphs and value

d speed = distance e time = distance for money.
time speed
+ When you use compound measures to make
comparisons, the measures you compare must all
be the same, e.g. km/h or $ per 100 g.

4 Length, mass, capacity and time 39