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Date November 2018 Marks available 2 Reference code 18N.2.AHL.TZ0.H_3
Level Additional Higher Level Paper Paper 2 Time zone Time zone 0
Command term Find Question number H_3 Adapted from N/A

Question

It is known that 56 % of Infiglow batteries have a life of less than 16 hours, and 94 % have a life less than 17 hours. It can be assumed that battery life is modelled by the normal distribution N ( μ , σ 2 ) .

Find the value of μ and the value of σ .

[6]
a.

Find the probability that a randomly selected Infiglow battery will have a life of at least 15 hours.

[2]
b.

Markscheme

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

use of inverse normal (implied by ±0.1509… or ±1.554…)       (M1)

P(X < 16) = 0.56

16 μ σ = 0.1509       (A1)

P(X < 17) = 0.94

17 μ σ = 1.554       (A1)

attempt to solve a pair of simultaneous equations       (M1)

μ = 15.9,   σ = 0.712      A1A1

 

[6 marks]

a.

correctly shaded diagram or intent to find P(X ≥ 15)       (M1)

= 0.895       A1

Note: Accept answers rounding to 0.89 or 0.90. Award M1A0 for the answer 0.9.

 

[2 marks]

b.

Examiners report

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

Syllabus sections

Topic 4—Statistics and probability » SL 4.9—Normal distribution and calculations
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Topic 4—Statistics and probability

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