Coal is carried from a mine in West Virginia to a power plant in New York in hop

Question

Coal is carried from a mine in West Virginia to a power plant in New York in hopper cars on a long train. The automatic hopper car loader is set to put 58 tons of coal into each car. The actual weights of coal loaded into each car are normally distributed, with mean ?-58 tons and standard deviation ?-1.1 ton. (a) What is the probability that one car chosen at random will have less than 57.5 tons of coal? (Round your answer to four decimal places.) (b) What is the probability that 21 cars chosen at random will have a mean load weight x of less than 57.5 tons of coal? (Round your answer to four decimal places.) (c) Suppose the weight of coal in one car was less than 57.5 tons. Would that fact make you suspect that the loader had slipped out of adjustment? Yes O No Suppose the weight of coal in 21 cars selected at random had an average x of less than 57.5 tons. Would that fact make you suspect that the loader had slipped out of adjustment? Why? O Yes, the probability that this deviation is random is very small. O Yes, the probability that this deviation is random is very large. No, the probability that this deviation is random is very small. O No, the probability that this deviation is random is very large.

Explanation / Answer

a)

P(X<57.5)=P(Z<(57.5-58)/1.1)=P(Z<-0.45)=0.3264 ( please try 0.3247 if this comes wrong due to rounding)

b)

P(Xbar<57.5)=P(Z<(57.5-58)/(1.1/sqrt(21))=P(Z<-2.08)=0.0188 ( please try 0.0186 if this comes wrong due to rounding)

c)

No (As probability is higher than 0.05)

Yes; the probability that this deviation is random is very small

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