Question 1182351: large construction firm estimates that the time required to complete a college complex is normally distribution with mean of 18 months and standard deviation of 2 months. What is the probability that it will take (i) at least one year and five month to complete it ? (ii) at most one year and eight months to complete it? (ii) between one year four months and one year ten months?
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! z=(x-mean)/sd
one year 5 months=17 months
z=(17-18)/2 =-0.5
for z > =-0.5 the probability is 0.6915
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for at most 1y8m is 20 months
z=(20-18)/2=1
probability z < 1 is 0.8413
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c is using 16 months and 22 months
can use the calculator here as well.
2ndVARS2normalcdf(16,22,18,2)ENTER, and that is low, high, the known mean, and the normal sd)
=0.8186 probability
That is also between -1 and +2 sd
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