Many electronics follow a failure rate described by an exponential probability density function (PDF). Solar panels are advertised to last 20 years or longer, but panels made in China are failing at a higher rate. The time-to-failure of this device is usually exponentially distributed with mean 13 years. What is the probability of failure in the first 6 years? The average time between accidents in a factory is 14 weeks. Find the probability that more than 15 weeks pass between accidents. Why is the probability that a continuous random variable equals a specific number zero? That is, why is P(X-b)-0 for any number b?