In a random sample of 50 babies 4 to 7 month old the average number of hours they slept per day turned out to be 14.2 hours with a standard deviation of 1.6 hours find and interpret a 90% confidence interval for the mean number of hours slept by babies at this age
90% = mean ± 1.645SEm
SEm = SD/√n
I'll let you do the calculations.