Question: According to a survey conducted by TD Ameritrade, one out of four investors has exchange-traded funds in his or her portfolio ( USA Today. January I I.2007). Consider a sample of 20 investors.
a. Compute the probability that exactly four investors have exchange-traded funds in their portfolios.
b. Compute the probability that at least two of the investors have exchange-traded funds in their portfolios.
c. If you found that exactly 12 of the investors have exchange-traded funds in their port-folios. would you doubt the accuracy of the survey results?
d. Compute the expected number of investors who have exchange-traded funds in their portfolios.