In the National Weekly Edition of the Washington Post (December 19-25, 2005), firstStreet, Inc. advertised an atomic digital watch from LaCrosse Technology. It is radio-controlled and maintains its accuracy by reading a radio signal from a WWVB radio signal from Colorado. It neither loses nor gains a second in 20 million years. It is powered by a 3-volt lithium battery expected to last three years. Suppose the life of the battery has a standard deviation of 0.3 years and is normally distributed.
a. Determine the probability that the watch's battery will last longer than 3.5 years.
b. Calculate the probability that the watch's battery will last more than 2.75 years.
c. Compute the length-of-life value for which 10% of the watch's batteries last longer.