Given a random variable X (time to receive service at BurgerLand) with mean μ unknown and standard deviation σx = 0.6 minutes, how large a sample should you take in order to estimate the mean (μx) within +/- 0.2 minutes with 95% confidence?

Question

Given a random variable X (time to receive service at BurgerLand) with mean μ unknown and standard deviation σx = 0.6 minutes, how large a sample should you take in order to estimate the mean (μx) within +/- 0.2  minutes with 95% confidence?

p0sitr0n · Answer

you want the width of your confidence interval to be 0.2=0.6/sqrt(n)*1.96
Solving gets you n~34.6 or n=35 rounding upwards.