19. The average lifetime of a certain type of light bulb is 500 hours. Assume that if the current light bulb burns out, it will get changed immediately. Please answer the following questions. a) Name the distribution and parameter(s) of the light bulb's life. b) What's the probability that a light bulb lasts more than 520 hours? c) If we know a light bulb is still working after 230 hours, what's the probability that it burns out before reaching 600 hours. (1) What is the average number of light bulbs that will be used in 2000 hours? e) What is the probability that there are between 4 and 6 light bulbs (inclusive) used in 2000 hours? i) If we know that there were 6 light bulbs used in 2000 hours, what's the probability that 2 were used in the last 400 hours