Date | May Specimen paper | Marks available | 6 | Reference code | SPM.1.AHL.TZ0.10 |
Level | Additional Higher Level | Paper | Paper 1 | Time zone | Time zone 0 |
Command term | Find | Question number | 10 | Adapted from | N/A |
Question
In a coffee shop, the time it takes to serve a customer can be modelled by a normal distribution with a mean of 1.5 minutes and a standard deviation of 0.4 minutes.
Two customers enter the shop together. They are served one at a time.
Find the probability that the total time taken to serve both customers will be less than 4 minutes.
Clearly state any assumptions you have made.
Markscheme
let TT be the time to serve both customers and TiTi the time to serve the iith customer
assuming independence of T1T1 and T2T2 R1
TT is normally distributed and T=T1+T2T=T1+T2 (M1)
E(T)=1.5+1.5=3E(T)=1.5+1.5=3 A1
Var(T)=0.42+0.42=0.32Var(T)=0.42+0.42=0.32 M1A1
P(T<4)=0.961P(T<4)=0.961 A1
[6 marks]