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Question
The time taken to assemble a car in a certain plant is a random variable having a normal distribution of 20 hours and a standard deviation of 2 hours. What is the probability that a car can be assembled at this plant in a period of time. Less than 19.5 hours?
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Solution
Let x denotes the time taken to assemable cars mean µ = 20 hours and S.D σ = 2 hours
The standard normal variate
z = `(x - mu)/sigma`
= `(x - 20)/2`
P(less than 19.5 hours) = P(X < 19.5)
When x = 19.5
z = `19.5/2`
= `(-0.5)/2`
= 0.25
P(X < 19.5) = P(Z < – 0.25)
= P(`-oo` < z < 0) – P(– 0.25 < z < 0)
= 0.5 – P(0 < z < 0.25)
= 0.5 – 0.0987
= 0.4013
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