Cambridge International Mathematics

b

c When x=70, y¼ 80 :

) we estimate the post-test score to be 80.

EXERCISE 22B

1 A class of 13 students was asked to record their times spent preparing for a test. The table below gives

their recorded preparation times and the scores that they achieved for the test.

Minutes spent preparing 75 30 35 65 110 60 40 80 56 70 50 110 18

Test score 25 31 30 38 55 20 39 47 35 45 32 33 34

a Which of the two variables is the independent variable?

b Calculate the mean timexand the mean scorey.

c Construct a scatter diagram for the data.

d Comment on the correlation between the variables.

e Copy and complete the following statements about the scatter diagram:

There appears to be a ............. , .................. correlation between theminutes spent preparingand

thetest score. This means that as the time spent preparing increases the scores ....................

f Plot (x,y) on the scatter diagram.

g Draw the line of best fit on the scatter diagram.

h

City Percentage Number

A 7 113

B 6 67

C 10 117

D 7 82

E 9 120

F 6 32

G 3 61

H 7 76

40

50

60

70

80

90

100

30 40 50 60 70 80 90

(x,y)

y

x

2 The table alongside shows thepercentage of unemployed adultsand

thenumber of major thefts per dayin eight large cities.

a Find the mean percentagexand the mean number of theftsy.

b Draw a scatter diagram for this data.

c Describe the association between thepercentage of unemployed

adultsand thenumber of major thefts per day.

d Plot (x,y) on the scatter diagram.

e Draw the line of best fit on the scatter diagram.

f Another city has8%unemployment. Estimate the number of

major thefts per day for that city.

If another student spent minutes preparing for the test, what would you predict his test score

to be?

25

460 Two variable analysis (Chapter 22)

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Y:\HAESE\IGCSE01\IG01_22\460IGCSE01_22.CDR Monday, 27 October 2008 2:14:48 PM PETER