Question 335567: The usual life of a computer terminal at a university computer center is known to be normally distributed with a mean of 3.25 years and a standard deviation of .5 years.
A. What proportion of computer terminals will have a useful life of at least 3 years?
B. Historically, 20% of the terminals have had a useful life less than the manufacture's advertised life. What is the manufacture's advertised life for the computer terminals?
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! The usual life of a computer terminal at a university computer center is known to be normally distributed with a mean of 3.25 years and a standard deviation of .5 years.
A. What proportion of computer terminals will have a useful life of at least 3 years?
z(3) = (3-3.25)/0.5 = -1/2
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P(x >= 3) = P(z > -1/2) = normalcdf(-1/2,1000) = 0.6915
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B. Historically, 20% of the terminals have had a useful life less than the manufacture's advertised life. What is the manufacture's advertised life for the computer terminals
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Draw a normal curve with u = 3.25
Find a point that has 20% of the population below 3.25
That point has a left-tail of 30%.
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Find the z-value with a 30% left-tail.
invNorm(0.30) = -0.5244
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Find the corresponding raw score value:
x = zs+u
x = -0.5244*0.5+3.25
x = 2.9878
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Cheers,
Stan H.
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