The probability that a new car battery functions for over 10,000 miles is .8, the probability that it functions for over 20,000 miles is .4, and the probability that it functions over 30,000 miles is .1. If a new battery is still working after 10,000 miles, what is the probability that:
a) It's total life will exceed 20,000 miles?
b) Its additional life will exceed 20,000 miles?