SSI chips, essential to the running of a computer system, fail in
accordance with a Poisson distribution with the rate of one chip
in about five weeks. If there are two spare chips on hand, and if
a new supply will arrive in eight weeks, what is the probability
that during the next eight weeks the system will be down for a
week or more, owing to a lack of chips?
在網路上也看到這題 但好像沒有正確的答案
不知道小弟這樣解對不對
將兩個chip當作獨立事件討論