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Date November 2017 Marks available 7 Reference code 17N.2.SL.TZ0.S_7
Level Standard Level Paper Paper 2 Time zone Time zone 0
Command term Find Question number S_7 Adapted from N/A

Question

The heights of adult males in a country are normally distributed with a mean of 180 cm and a standard deviation of σ  cm . 17% of these men are shorter than 168 cm. 80% of them have heights between ( 192 h )  cm and 192 cm.

Find the value of h .

Markscheme

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

finding the z -value for 0.17     (A1)

eg z = 0.95416

setting up equation to find σ ,     (M1)

eg z = 168 180 σ ,   0.954 = 12 σ

σ = 12.5765     (A1)

EITHER (Properties of the Normal curve)

correct value (seen anywhere)     (A1)

eg P ( X < 192 ) = 0.83 ,  P ( X > 192 ) = 0.17

correct working     (A1)

eg P ( X < 192 h ) = 0.83 0.8 ,  P ( X < 192 h ) = 1 0.8 0.17 ,

P ( X > 192 h ) = 0.8 + 0.17

correct equation in h

eg ( 192 h ) 180 12.576 = 1.88079 ,   192 h = 156.346     (A1)

35.6536

h = 35.7     A1     N3

OR (Trial and error using different values of h)

two correct probabilities whose 2 sf will round up and down, respectively, to 0.8     A2

eg P ( 192 35.6 < X < 192 ) = 0.799706 ,  P ( 157 < X < 192 ) = 0.796284 ,

P ( 192 36 < X < 192 ) = 0.801824

h = 35.7      A2

[7 marks]

Examiners report

[N/A]

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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