Question: Estimate average amount of time a worker requires to assemble a new electronic component.

Shortest time taken is 10 mins to assembly component. Longest time is 22min. Using these observations, how large a sample of workers should she take if she wishes to estimate the mean assembly time to within 20 seconds.

Additional Info: Assume that confidence level is to be 95%. Also. Since we must assume normality, the standard deviation can be well-estimated by dividing the range of observed values by 4- so you can get your hands on sigma( estimate, but good enough). Be aware of not mixing up time units- minutes and seconds.