Suppose a car manufacturer believes its windscreen wipers will last on average for three years on their cars if driven by a typical driver in the province. moreover, the manufacturer believes the lifetime of the wipers under such conditions is normally distributed with a standard deviation of two years. find the probability that, if on a car driven by a typical driver, a windscreen wiper lasts for a time that is not within 1.7 years of the mean lifetime.
the probability is: ?