A Nielsen study indicates that mobile subscribers between 18 and 24 years of age spend a substantial amount of time watching video on their devices, reporting a mean of 325 minutes per month. (Data extracted from bit.ly/ NfLzE9.) Assume that the amount of time watching video on a mobile device per month is normally distributed and that the standard deviation is 50 minutes.
a. What is the probability that an 18- to 24-year-old mobile subscriber spends less than 250 minutes watching video on his or her mobile device per month?
b. What is the probability that an 18- to 24-year-old mobile subscriber spends between 250 minutes and 400 minutes watching video on his or her mobile device per month?
c. What is the probability that an 18- to 24-year-old mobile subscriber spends more than 400 minutes watching video on his or her mobile device per month?
d. 1% of all 18- to 24-year-old mobile subscribers will spend less than how many minutes watching video on his or her mobile device per month?