a.The annual salary for the CEOs from the Forbes 500 ranging from a minimum of $3.123 to $68.888 million and it is known to be normally distributed. A random sample of 20 CEOs was selected. The average and standard deviation for this sample of CEOs are $11.765 million and $2.123 million respectively. Construct a 90% confidence interval for the mean annual salary of all Forbes 500 CEOs.

b. Twenty-five percent of all cellphones of a certain type are submitted for service while under warranty. Of these, 70% can be repaired whereas the other 30% must be replaced with new units. If a company purchases ten of these cellphones, what is the probability that at most one will end up being replaced under warranty?