According to the Nielsen Company, teenagers between the ages of 13 and 17 send an average of 3340 text messages per month, or more than six texts every waking hour. You plan to draw a random sample of 900 teenagers from this 13-to-17 population. Assuming that the standard deviation for the population is 660 texts per month,

a. What is the probability that the average number of texts for your sample will be somewhere between 3300 and 3400?

b. How likely is it that the sample average will be within ±2 standard deviations (that is, ±2σxσx) of the population average?

c. It is 90% likely that the sample average number of texts will be within ± ____ texts of the population average.