A study indicates that 18 to 24 year olds spend a mean of 135 minutes watching video on their smart phones per day. assume that the amount of time watching video on a smart phone per day is normally distributed and that the standard deviation is 10 minutes.

a) what is the probability that an 18 - 24 year old spends between 120 to 145 minutes watching video on his or her smart phone per day?

b) five percent of all 18- 24 years old will spend less than how many minutes watching video on his or her smart phone per day?

c) Find the interval symmetrically distribute around the mean that contains 95% of the amounts of time spent watching video on smart phones per day for 18 - 24 years olds.