Date | May 2021 | Marks available | 1 | Reference code | 21M.1.AHL.TZ2.15 |
Level | Additional Higher Level | Paper | Paper 1 | Time zone | Time zone 2 |
Command term | State | 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.
Find the probability that Sheila will make a type I error in her test conclusion.
Sheila finds 126 coffees were sold during the 5-hour period.
State Sheila’s conclusion to the test. Justify your answer.
Markscheme
H0: m=110, H1: m>110 A1
Note: Accept other appropriate variables for the mean.
Accept 22 in place of 110.
[1 mark]
P(X≥128)=0.05024 (M1)(A1)
P(X≥129)=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]
X~Po(110)
P(X≥126)=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]