In: Statistics and Probability
The manager of a local fast-food restaurant is concerned about customers who ask for a water cup when placing an order but fill the cup with a soft drink from the beverage fountain instead of filling it with water. The manager selected a random sample of 50 customers who asked for a water cup when placing an order and found that 8 of those customers filled the cup with a soft drink from the beverage fountain.
(a) Find the sample size, and the proportion of customers who ordered water and took a soft drink (�). Are the conditions for the normal curve satisfied? Show your calculations.
(b) Construct a 98% confidence interval for the proportion of all customers who, having asked for a water cup with their order, will fill the cup with a soft drink from the beverage fountain.
(c) If we want to cut the width of the confidence interval in half (keeping the same confidence level and assuming the sample proportion will be the same), how many customers will we have to sample?