Apps. and Interpretation for IBDP Maths Ebook 1 | Page 283

(c)
Copy and complete the probability distribution table.
X 0 5 10
P( X � x)
[3]
(d)
Find the expected cost for Petr for both days.
[2]
Solution
(a) (i) P( A�B) � (0.2)(0.9)
(A1) for substitution
P( A�B) � 0.18
A1 N2
(ii) P( B) � P( A� B) � P( A�
� B)
(M1) for valid approach
P( B) �0.18 � (0.8)(0.25)
P( B) � 0.38
A1 N2
(b) (i) The required probability
�P( A��
B�)
� (0.8)(0.75)
(A1) for substitution
� 0.6
A1 N2
[4]
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(c)
(d)
(ii)
The required probability
� P( A�
| B)
(M1) for valid approach
P( A��
B)
�
P( B)
(0.8)(0.25)
� (A1) for substitution
0.38
10
� A1 N3
19
X 0 5 10
P( X � x)
0.04 0.32 0.64
The expected cost
� (0)(0.04) � (5)(0.32) � (10)(0.64)
(A1) for substitution
� $8
A1 N2
A3
N3
[5]
[3]
[2]
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