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Probability (page 101)
1 (a)
Ellen
Schweta
Model answers
0 . 8
Score
0 . 7
Score
0 . 2
Miss
0 . 8
Score
0 . 3
Miss
0 . 2
Miss
(b) (i) 0·7 × 0·8 = 0·56
(ii) 0·7 × 0·2 + 0·3 × 0·8 = 0·38
6 4
2 1 1 3
2 (a) –– and –– on first set of branches, – , – , – , – on second
10 10
3 3 4 4
set with ‘goes’, ‘not go’ or other suitable labels.
6 2 2
(b) (i) –– × –3 = –5 or equivalent
10
4 3 3
(ii) –– × – = –– or equivalent
10 4 10
6 5 1
3 (a) –– × –– = – or equivalent
15 14 7
4 3 5 4 31
(b) (a) + –– × –– + –– × –– = –––
15 14 15 14 105
74
(c) 1 – (b) = –––
105
1 1
4 (a) –6 × –6 = 36
5 –6
1 ––
5 –
6
(b) (i) × × ... n times = ( ) n
(ii) P(at least 1 six) = 1 – P(no six)
5 –
6
5 –
6
= 1 – ( ) n
5 (a)
Box A
Box B
50%
Red
Red
15%
Blue
20%
35%
Black
50%
Blue
50%
15%
Red
Blue
35%
Black
30%
50%
Red
Black
15%
Blue
35%
Black
(b) 0·2 × 0·5 = 0·1
= 10%
(c) 0·2 × 0·5 + 0·5 × 0·15 + 0·3 × 0·35
= 0·1 + 0·075 + 0·105
= 0·28
= 28%
26
IGCSE Revision Guide for Mathematics Model Answers © 2004, Hodder & Stoughton Educational