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Date May 2017 Marks available 2 Reference code 17M.1.AHL.TZ1.H_10
Level Additional Higher Level Paper Paper 1 Time zone Time zone 1
Command term Calculate Question number H_10 Adapted from N/A

Question

The continuous random variable X has a probability density function given by

f ( x ) = { k sin ( π x 6 ) , 0 x 6 0 , otherwise .

Find the value of k .

[4]
a.

By considering the graph of f write down the mean of X ;

[1]
b.i.

By considering the graph of f write down the median of X ;

[1]
b.ii.

By considering the graph of f write down the mode of X .

[1]
b.iii.

Show that P ( 0 X 2 ) = 1 4 .

[4]
c.i.

Hence state the interquartile range of X .

[2]
c.ii.

Calculate P ( X 4 | X 3 ) .

[2]
d.

Markscheme

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

attempt to equate integral to 1 (may appear later)     M1

k 0 6 sin ( π x 6 ) d x = 1

correct integral     A1

k [ 6 π cos ( π x 6 ) ] 0 6 = 1

substituting limits     M1

6 π ( 1 1 ) = 1 k

k = π 12 A1

[4 marks]

a.

mean = 3     A1

 

Note:     Award A1A0A0 for three equal answers in ( 0 ,   6 ) .

 

[1 mark]

b.i.

median = 3     A1

 

Note:     Award A1A0A0 for three equal answers in ( 0 ,   6 ) .

 

[1 mark]

b.ii.

mode = 3     A1

 

Note:     Award A1A0A0 for three equal answers in ( 0 ,   6 ) .

 

[1 mark]

b.iii.

π 12 0 2 sin ( π x 6 ) d x     M1

= π 12 [ 6 π cos ( π x 6 ) ] 0 2      A1

 

Note:     Accept without the π 12 at this stage if it is added later.

 

π 12 [ 6 π ( cos π 3 1 ) ]      M1

= 1 4      AG

[4 marks]

c.i.

from (c)(i) Q 1 = 2      (A1)

as the graph is symmetrical about the middle value x = 3 Q 3 = 4      (A1)

so interquartile range is

4 2

= 2      A1

[3 marks]

c.ii.

P ( X 4 | X 3 ) = P ( 3 X 4 ) P ( X 3 )

= 1 4 1 2      (M1)

= 1 2      A1

[2 marks]

d.

Examiners report

[N/A]
a.
[N/A]
b.i.
[N/A]
b.ii.
[N/A]
b.iii.
[N/A]
c.i.
[N/A]
c.ii.
[N/A]
d.

Syllabus sections

Topic 4—Statistics and probability » SL 4.6—Combined, mutually exclusive, conditional, independence, prob diagrams
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Topic 4—Statistics and probability » SL 4.7—Discrete random variables
Topic 4—Statistics and probability

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