Cell phone usage in Vietnam has grown dramatically in the last few years, drawing the interest of a number of international telecommunications companies. A study done by the country’s Communications Ministry reports that the average time that cell phone subscribers spent on their cell phone during the past year was 48.3 hours, with a standard deviation of 14 hours. Assume the usage distribution is normal.
a. What percentage of subscribers spent more than 60 hours on their cell phone during the year?
b. What percentage of subscribers spent less than 50 hours on their cell phone during the year?
c. What percentage of subscribers spent between 30 and 70 hours on their cell phone during the year?
d. The company is planning to offer a reduced rate plan for any subscribers who used their phone more than 65 hours during the year. What percent-age of users would qualify?