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Date May 2018 Marks available 2 Reference code 18M.2.AHL.TZ2.H_8
Level Additional Higher Level Paper Paper 2 Time zone Time zone 2
Command term Find Question number H_8 Adapted from N/A

Question

The random variable X has a binomial distribution with parameters n and p.
It is given that E(X) = 3.5.

Find the least possible value of n.

[2]
a.

It is further given that P(X ≤ 1) = 0.09478 correct to 4 significant figures.

Determine the value of n and the value of p.

[5]
b.

Markscheme

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

np = 3.5      (A1)

p ≤ 1 ⇒ least n = 4       A1

[2 marks]

a.

(1 − p)n + np(1 − p)n−1 = 0.09478     M1A1

attempt to solve above equation with np = 3.5     (M1)

n = 12,  p 7 24 (=0.292)     A1A1

Note: Do not accept n as a decimal.

[5 marks]

b.

Examiners report

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

Syllabus sections

Topic 4—Statistics and probability » SL 4.8—Binomial distribution
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Topic 4—Statistics and probability

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