Answer to Question #336819 in Statistics and Probability for Rival

Question #336819

A normal population has a mean of 50 and standard distribution of 10. Selecting 16 sample compute probability of sample mean



a) greater than 60



b) less than 45



c) between 45 and 60

1
Expert's answer
2022-05-04T15:04:07-0400

We have a normal distribution, μ=50,σ=10,n=16.μ=50,σ=10,n=16.

Let's convert it to the standard normal distribution.

zˉ=xˉμσ/n.\bar{z}=\cfrac{\bar{x}-\mu}{\sigma/\sqrt{n}}.


a) zˉ1=605010/16=4,P(Xˉ>60)==P(Zˉ>4)==1P(Zˉ<4)==11=0 (from z-table).\text{a) } \bar{z}_1=\cfrac{60-50}{10/\sqrt{16}}=4,\\ P(\bar{X}>60)=\\ =P(\bar{Z}>4)=\\ =1-P(\bar{Z}<4)=\\ =1-1=0\text{ (from z-table).}


b) zˉ2=455010/16=2,P(Xˉ<45)==P(Zˉ<2)==0.0228 (from z-table).\text{b) } \bar{z}_2=\cfrac{45-50}{10/\sqrt{16}}=-2,\\ P(\bar{X}<45)=\\ =P(\bar{Z}<-2)=\\ =0.0228\text{ (from z-table).}


c) P(45<Xˉ<60)==P(2<Zˉ<4)==P(Zˉ<4)P(Zˉ<2)==10.0228=0.9772.\text{c) } P(45<\bar{X}<60)=\\ =P(-2<\bar{Z}<4)=\\ =P(\bar{Z}<4)-P(\bar{Z}<-2)=\\ =1-0.0228=0.9772.


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