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rest of the times Points) al car repair garage cames out the work on time for on

ID: 3074151 • Letter: R

Question

rest of the times Points) al car repair garage cames out the work on time for only 80% of there arJobs, and is late the rest of the time. Historical data shows that: If the repair is made on time, there is a probability of 0.75 that the repair work is satisfactory. If the repair work is done late, the probability of the work being satisfactory is 0.6. For a randomly selected repair job at the garage, find the probability of the following: (a) That the repair work is both done on-time, and is satisfactory. (b) That the repair work is neither on-time nor satisfactory

Explanation / Answer

Let Event W: Car repair garrage carries out the work on time
P(W) = 0.80
P(Wc) = 0.20
Let Event S: Repair work is satisfactory
Given: P(S | W) = 0.75
P(S | Wc) = 0.60
(a) Probability that repair work is both satisfactory and done on time:
P(W S)
P(S | W) = P(SW) / P(W)
P(SW) = P(W).P(S|W) = 0.80 x 0.75 = 0.60
(b) Probability that the repair work is neither on time nor satisfactory
P(WcSc) = 1 - P(WUS)
P(W U S) = P(W) + P(S) - P(WS)
Using total law: P(S) = P(W)P(S|W) + P(Wc)P(S|Wc)
P(S) = (0.80 x 0.75) + (0.20 x 0.60) = 0.72
P(WUS) = 0.80 + 0.72 - 0.60 = 0.92
P(WcSc) = 1 - 0.92 = 0.08