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**ulysses123** A certain part of a machine can be in one of two states: working (W) or undergoing

repair (R). A working part fails during the course of a day with probability a; assume

that failure occurs at the end of the day so that the part can be labelled as in working

condition for that day. Having failed, it undergoes repair on the following working day.

The probability that a part undergoing repair is in working order by the start of the

following working day is b.

Assume that the part is in working condition on Monday morning. What is the probability

that it is working on Wednesday (2 days later)?

I have gotten (1-a)^2+(1-a)ab but i am not sure if i have done it wrong. I have basically used a tree diagram and used the appropriate branches.Can anyone check my solution because there is no answer for the odd questions in the book