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Date May 2018 Marks available 4 Reference code 18M.2.SL.TZ1.S_5
Level Standard Level Paper Paper 2 Time zone Time zone 1
Command term Find Question number S_5 Adapted from N/A

Question

Two events A and B are such that P(A) = 0.62 and P ( A B ) = 0.18.

Find P(AB′ ).

[2]
a.

Given that P((AB)′) = 0.19, find P(A |B).

[4]
b.

Markscheme

* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.

valid approach

eg  Venn diagram, P(A) − P (AB), 0.62 − 0.18      (M1)

P(AB' ) = 0.44      A1 N2

[2 marks]

a.

valid approach to find either P(B′ ) or P(B)      (M1)

eg   (seen anywhere), 1 − P(A ∩ B) − P((A ∪ B)′)

correct calculation for P(B′ ) or P(B)      (A1)

eg  0.44 + 0.19, 0.81 − 0.62 + 0.18

correct substitution into  P ( A B ) P ( B )       (A1)

eg   0.44 0.19 + 0.44 , 0.44 1 0.37

0.698412

P(A |B) =  44 63   (exact), 0.698     A1 N3

[4 marks]

b.

Examiners report

[N/A]
a.
[N/A]
b.

Syllabus sections

Topic 4—Statistics and probability » SL 4.5—Probability concepts, expected numbers
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Topic 4—Statistics and probability » SL 4.6—Combined, mutually exclusive, conditional, independence, prob diagrams
Topic 4—Statistics and probability

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