Question

Management is exploring adding more cashiers at the check-out counter of a supermarket to reduce the waiting time of customers. Based on the available information the waiting times have a standard deviation of approximately 5.6 min. If management wants to estimate the waiting time to within 2 min. with 90% confidence, how large a sample must be chosen? Can you write them with excel formulas? Show your work step by step.

Answer 1

We have given here,              
              
Population standard deviation =5.6 minute
Margin of error =E=2 minute
Level of significance =1-0.90=0.1
Z critical value is (by using Z table)=1.645
Sample size formula is               


=21.22  

In Excel =((1.645*5.6)/2)^2