User interface language: English | Español

Date May 2018 Marks available 2 Reference code 18M.2.AHL.TZ2.H_3
Level Additional Higher Level Paper Paper 2 Time zone Time zone 2
Command term Find Question number H_3 Adapted from N/A

Question

The random variable X has a normal distribution with mean μ = 50 and variance σ 2 = 16 .

Sketch the probability density function for X, and shade the region representing P(μ − 2σ < X < μ + σ).

[2]
a.

Find the value of P(μ − 2σ < X < μ + σ).

[2]
b.

Find the value of k for which P(μkσ < X < μ + kσ) = 0.5.

[2]
c.

Markscheme

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

normal curve centred on 50      A1

vertical lines at x = 42 and x = 54, with shading in between       A1

[2 marks]

a.

P(42 X < 54) (= P(− 2 Z < 1))     (M1)

= 0.819       A1

[2 marks]

b.

P(μ − kσ < X < μ + kσ) = 0.5 ⇒ P(X < μ + kσ) = 0.75      (M1)

k = 0.674       A1

Note: Award M1A0 for k = −0.674.

[2 marks]

c.

Examiners report

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

Syllabus sections

Topic 4—Statistics and probability » SL 4.9—Normal distribution and calculations
Show 181 related questions
Topic 4—Statistics and probability

View options