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Date May 2012 Marks available 2 Reference code 12M.2.hl.TZ2.5
Level HL only Paper 2 Time zone TZ2
Command term Find Question number 5 Adapted from N/A

Question

The random variable X has the distribution Po(m)Po(m) .

Given that P(X=5)=P(X=3)+P(X=4)P(X=5)=P(X=3)+P(X=4), find

the value of m ;

[3]
a.

P (X > 2) .

[2]
b.

Markscheme

P(X=5)=P(X=3)+P(X=4)P(X=5)=P(X=3)+P(X=4)

emm55!=emm33!+emm44!emm55!=emm33!+emm44!     M1(A1)

m25m20=0m25m20=0

m=5+1052=(7.62)m=5+1052=(7.62)     A1

[3 marks]

a.

P(X>2)=1P(X2)     (M1)

=10.018...

=0.982     A1

[2 marks]

b.

Examiners report

Again this proved to be a successful question for many candidates with a good proportion of wholly correct answers seen. It was good to see students making good use of the calculator.

a.

Again this proved to be a successful question for many candidates with a good proportion of wholly correct answers seen. It was good to see students making good use of the calculator.

b.

Syllabus sections

Topic 5 - Core: Statistics and probability » 5.6 » Poisson distribution, its mean and variance.
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