Question 5

A consultant is tasked with studying the purchasing habits of customers in an Indonesian coffee shop which specialises in Kopi Luwak. They select a random sample of 66 customers during a certain week and find that the mean amount spent was 291,000 rupiah, with a standard deviation of 61,000 rupiah. They also found that 40 customers would ‘strongly recommend’ the coffee shop to their family and friends. 

(a) At the 0.05 level of significance, is there evidence that the population mean amount spent was different from 268,000 rupiah? Show all your working and clearly indicate the assumptions used. 

(b) At the 0.05 level of significance, is there evidence that more than 50% of all the customers say they would ‘strongly recommend’ the coffee shop to their family and friends? Show all your workings and assumptions used.