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Date May 2021 Marks available 2 Reference code 21M.2.SL.TZ2.4
Level Standard Level Paper Paper 2 Time zone Time zone 2
Command term Find Question number 4 Adapted from N/A

Question

It is known that the weights of male Persian cats are normally distributed with mean 6.1kg and variance 0.52kg2.

A group of 80 male Persian cats are drawn from this population.

Sketch a diagram showing the above information.

[2]
a.

Find the proportion of male Persian cats weighing between 5.5kg and 6.5kg.

[2]
b.

Determine the expected number of cats in this group that have a weight of less than 5.3kg.

[3]
c.

It is found that 12 of the cats weigh more than xkg. Estimate the value of x.

[3]
d.

Ten of the cats are chosen at random. Find the probability that exactly one of them weighs over 6.25kg.

[4]
e.

Markscheme

                A1A1


Note: Award A1 for a normal curve with mean labelled 6.1 or μ, A1 for indication of SD (0.5): marks on horizontal axis at 5.6 and/or 6.6 OR μ-0.5 and/or μ+0.5 on the correct side and approximately correct position.

[2 marks]

a.

X~N6.1, 0.52

P5.5<X<6.5  OR  labelled sketch of region                (M1)

=0.673  0.673074                A1


[2 marks]

b.

PX<5.3= 0.0547992                (A1)

0.0547992×80                (M1)

=4.38   4.38393                A1


[3 marks]

c.

0.15  OR  0.85               (A1)

PX>x=0.15  OR  PX<x=0.85  OR  labelled sketch of region                (M1)

6.62   6.61821                A1


[3 marks]

d.

PX>6.25= 0.382088               (A1)

recognition of binomial                (M1)

e.g. B(10, 0.382088)

0.0502   0.0501768                A2


[4 marks]

e.

Examiners report

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

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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