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Date May 2021 Marks available 4 Reference code 21M.1.AHL.TZ2.15
Level Additional Higher Level Paper Paper 1 Time zone Time zone 2
Command term Find Question number 15 Adapted from N/A

Question

The number of coffees sold per hour at an independent coffee shop is modelled by a Poisson distribution with a mean of 22 coffees per hour.

Sheila, the shop’s owner wants to increase the number of coffees sold in the shop. She decides to offer a discount to customers who buy more than one coffee.

To test how successful this strategy is, Sheila records the number of coffees sold over a single 5-hour period. Sheila decides to use a 5% level of significance in her test.

State the null and alternative hypotheses for the test.

[1]
a.

Find the probability that Sheila will make a type I error in her test conclusion.

[4]
b.

Sheila finds 126 coffees were sold during the 5-hour period.

State Sheila’s conclusion to the test. Justify your answer.

[2]
c.

Markscheme

H0:m=110, H1:m>110             A1

Note: Accept other appropriate variables for the mean.
         Accept 22 in place of 110.


[1 mark]

a.

PX128=0.05024          (M1)(A1)

PX129=0.04153                (M1)

(probability of making a type I error is)  0.0415           A1


Note:
If other probabilities are seen, the final A1 cannot be awarded unless 0.0415 is clearly identified as the final answer.


[4 marks]

b.

X~Po110

PX126=0.072>0.05  OR  recognizing 126<129 or 128           R1

so there is insufficient evidence to reject H0           A1

(ie there is insufficient evidence to suggest that the number of coffees being sold has increased)


Note:
Accept ‘Accept H0’.
          Do not award R0A1.


[2 marks]

c.

Examiners report

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

Syllabus sections

Topic 4—Statistics and probability » AHL 4.17—Poisson distribution
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