Apps. and Interpretation for IBDP Maths Ebook 1 | Page 264

Your Practice Set – Applications and Interpretation for IBDP Mathematics
74
Paper 1 – Probability Formulae
Example
Events A and B are independent with P( A� B) � P( A�
� B) � 0.1.
(a) Find P( B ) .
(b) Find P( A ) .
(c) Find P( A� B)
.
[2]
[2]
[2]
Solution
(a) P( B) � P( A� B) � P( A�
� B)
(M1) for valid approach
P( B) �0.1�
0.1
P( B) � 0.2
A1 N2
(b) P( A� B) � P( A) � P( B)
0.1 �P( A) � 0.2
(A1) for substitution
P( A) � 0.5
A1 N2
(c) P( A� B) � P( A) � P( B) � P( A�
B)
P( A� B) � 0.5 � 0.2 � 0.1
(A1) for substitution
P( A�B) � 0.6
A1 N2
[2]
[2]
[2]
Exercise 74
1. Events A and B are independent with P( A�B) � 0.08 and P( A�B�) � 0.12 .
(a) Find P( A ) .
(b) Find P( B ) .
(c) Find P( A� B)
.
[2]
[2]
[2]
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