(2) (10 pts) Suppose a particular manufacturer of concrete masonry units (CMUs)
ID: 3057243 • Letter: #
Question
(2) (10 pts) Suppose a particular manufacturer of concrete masonry units (CMUs) claims that the average compressive strength of batches of CMUs made with one of their concrete mixes is normally distributed with a mean of 2000 psi and a standard deviation of 150 psi. a) (5 pts) What is the probability that a batch provided by this company has an e strength that exceeds 2200 psi? b) (5 pts) If the specifications for your project require that batches of this type of CMU must have an average compressive strength that exceeds 1900 psi, what fraction of delivered batches will likely fail this requirement?Explanation / Answer
Solution2A:
given mean=2000
sd=150
P(X>2200)
z=x-mean/ssd
z=2200-2000/150
=200/150
=1.333333
P(Z>1.33)
1-P(Z<1.33)
=1-0.9082
=0.0918
= 0.09121127
ANSWER:0.09121127
THE PROBABILITY THAT A BATCH PROVIDED BY THIS COMPANY HAS AN AVERAGE COMPRESSIVE STRENGTH THAT EXCEEDS 2200 PSI IS 0.0918
Solutionb:
x=1900
z=1900-2000/150
=-0.6666667
P(Z>-0.67)
=P(Z<0.67)
=0.7486
ANSWER:0.7486
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