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Date November 2018 Marks available 3 Reference code 18N.1.AHL.TZ0.H_1
Level Additional Higher Level Paper Paper 1 Time zone Time zone 0
Command term Show that Question number H_1 Adapted from N/A

Question

Consider two events, A and B, such that P(A)=P(AB)=0.4 and P(AB)=0.1.

By drawing a Venn diagram, or otherwise, find P(AB).

[3]
a.

Show that the events A and B are not independent.

[3]
b.

Markscheme

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

        (M1)

Note: Award M1 for a Venn diagram with at least one probability in the correct region.

 

EITHER

P(AB)=0.3     (A1)

P(AB)=0.3+0.4+0.1=0.8     A1

OR

P(B)=0.5     (A1)

P(AB)=0.5+0.40.1=0.8     A1

 

[3 marks]

a.

METHOD 1

P(A)P(B)=0.4×0.5        (M1)

= 0.2      A1

statement that their P(A)P(B)P(AB)      R1

Note: Award R1 for correct reasoning from their value.

⇒ A, B not independent     AG

 

METHOD 2

P(A|B)=P(AB)P(B)=0.10.5        (M1)

= 0.2      A1

statement that their P(A|B)P(A)      R1

Note: Award R1 for correct reasoning from their value.

⇒ A, B not independent     AG

Note: Accept equivalent argument using P(B|A)=0.25.

 

[3 marks]

b.

Examiners report

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

Syllabus sections

Topic 4—Statistics and probability » SL 4.6—Combined, mutually exclusive, conditional, independence, prob diagrams
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Topic 4—Statistics and probability

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