Turn over 19 Question 7 continued (a) State two reasons why the mean sampled delays may be modelled as 2 2 2.45 3.10 N , and N , 55 56 S B μ μ             where μS and μB are the mean delays on all ‘morning rush’ trains from Southend‑on‑Sea and Brighton respectively. (2) _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ (b) Conduct a hypothesis test using Richard’s data to investigate whether the mean delay on ‘morning rush’ trains from Southend‑on‑Sea is less than zero (on average trains arrive early). (6) _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________