17. A recent newspaper article reported the results of a survey of well-educated suburban parents. The responses to one question indicated that by age 2, children were watching an average of  60 minutes of television each day. Assuming that the distribution of television-watching times is normal with a standard deviation of  20 minutes, find each of the following proportions.

a. What proportion of 2-year-old children watch more than 90 minutes of television each day?

b. What proportion of 2-year-old children watch less than 20 minutes a day?