A researcher wants to estimate the number of teachers who have changed careers after their first year of teaching. How many 1st year teachers does he need to sample in order to be 95% confident that his estimate for the mean number of teachers will be within 3 teachers of the true mean? The standard deviation is 2 teachers.

2people are trying different phones to see which one has the better talk time. chatlong has an average of 18 hours with a standard deviation of 2 hours and talk-a-lot has an average of 20 hours with a standard deviation of 3. the two people who tested their phones both got 20 hours of use on their phones. for the z-scores i got 1 for the chatlong company and 0 for talk-a-lot. what is the percentile for each z-score?