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Date May 2015 Marks available 3 Reference code 15M.2.hl.TZ2.9
Level HL only Paper 2 Time zone TZ2
Command term Find Question number 9 Adapted from N/A

Question

Natasha lives in Chicago and has relatives in Nashville and St. Louis.

Each time she visits her relatives, she either flies or drives.

When travelling to Nashville, the probability that she drives is 45, and when travelling to St. Louis, the probability that she flies is 13.

Given that the probability that she drives when visiting her relatives is 1318, find the probability that for a particular trip,

she travels to Nashville;

[3]
a.

she is on her way to Nashville, given that she is flying.

[3]
b.

Markscheme

attempt to set up the problem using a tree diagram and/or an equation, with the unknown x     M1

45x+23(1x)=1318     A1

4x52x3=131823

2x15=118

x=512     A1

[3 marks]

a.

attempt to set up the problem using conditional probability     M1

EITHER

512×1511318     A1

OR

512×15112+736     A1

THEN

=310     A1

[3 marks]

Total [6 marks]

b.

Examiners report

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

Syllabus sections

Topic 5 - Core: Statistics and probability » 5.4 » Use of Bayes’ theorem for a maximum of three events.

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