Expert Q&A; Done Name: Quiz March 21, 2017 L. (+2)a While travelling in Chile, y

Question

Expert Q&A; Done Name: Quiz March 21, 2017 L. (+2)a While travelling in Chile, you are deeply impressed at the precautions that construction companies take to ensure that buildings do not collapse in the frequent evere earthquakes (the building at right collapsed in an 8.8 Richter scale quake). Speaking with your local friendly construction engineer, you discover that the compressive strength of concrete is normally distributed with -2500 pui·nd -50psi. Find the probability that a random sample of n-5 specimens will have a sample mean diameter that falls in the interval from 2499 psi to 2510 psi. (2) b. With-5, what is the standard error of the sample mean (that is, what is (+2)c. Irwe wished to change , to 100psi, how many samples should be taken? 7)

Explanation / Answer

a) for here std error of mean =std deviaiton/(n)1/2 =50/(5)1/2 =22.36

hence probability=P(2499<Xbar<2510)=P((2499-2500)/22.36<Z<(2510-2500)/22.36)=P(-0.04472<Z<0.4472)

=0.6726-0.4821 =0.1905

b) std error of mean ==std deviaiton/(n)1/2 =50/(5)1/2 =22.36

c) from above for doubling the std deviaiton; we need to increase sample size 4 times

therefore new required smaple size =4*5=20

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