Answer to Question #196704 in Statistics and Probability for jack

Question #196704

A car dealership has both Electric and Internal Combustion Engine (ICE) vehicles available for sale. 30% of customers looking to purchase a new car are interested in Electric vehicles, while the rest want ICE vehicles. On a particular day, the dealership had 17 people coming in to purchase a new car. What is the probability that the number of people who are interested in an Electric vehicle is more than two standard deviations away from the mean value?


1
Expert's answer
2021-05-24T11:31:34-0400

Let X be the number of people.


XB(n,p)XB(17,0.30)X\sim B(n,p) \\ X\sim B(17,0.30)\\


Mean E(X)=np=17×0.3=5.1E(X)=np=17\times 0.3=5.1


Standard deviation-


s=np(1p)=17×0.3×(10.3)=1.8894s=\sqrt{np(1-p)}=\sqrt{17\times 0.3\times (1-0.3)}=1.8894


By using Normal approximation of Binomal distribution.


XN(μ=5.1,σ=1.8894)X\sim N(\mu=5.1,\sigma=1.8894)


Probability that the number of people who are interested in an Electric vehicle is more than two standard deviations away from the mean value is-


=P(X<μ2σ)+P(X>μ+2σ)=P(Z<2)+P(z>2)=0.0228+0.0228=0.0456=P(X<\mu-2\sigma)+P(X>\mu+2\sigma) \\[9pt] =P(Z<-2)+P(z>2) \\[9pt] =0.0228+0.0228\\[9pt]=0.0456


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