Confidence Intervals, Sample Size


The mean weight of trucks traveling on a particular si not known. A highway inspector needs an estimate of the mean. a random sample of 49 trucks passing the weighing station and finds the mean is 15.8 tons and standard deviation of 3.9 tons. what is the 95% interval of population mean?

A poll is being conducted as to determine whether of not patients prefer one hospital over another. What sample size do I need to be 95% confident and within 5 points of the true mean proportion if the proportion in the past has been near 50%?

first time using site. not sure ho this works. however need help.