Question #180897

A random sample is size n = 2 are drawn from a finite population consisting of the numbers 3,4,5,6 and 7


1
Expert's answer
2021-04-15T06:30:42-0400

1. Mean


μ=3+4+5+6+75=5\mu=\dfrac{3+4+5+6+7}{5}=5

Variance


σ2=15((35)2+(45)2+(55)2\sigma^2=\dfrac{1}{5}\big((3-5)^2+(4-5)^2+(5-5)^2

(65)2+(75)2)=2(6-5)^2+(7-5)^2\big)=2


Standard deviation


σ=σ2=21.4142\sigma=\sqrt{\sigma^2}=\sqrt{2}\approx1.4142



2. We have population values 3,4,5,6,7,3,4,5,6,7, population size N=5N=5 and sample size n=2.n=2. Thus, the number of possible samples which can be drawn without replacement is


(Nn)=(52)=10\dbinom{N}{n}=\dbinom{5}{2}=10SampleSampleSample meanNo.values(Xˉ)13,43.523,5433,64.543,7554,54.564,6574,75.585,65.595,76106,76.5\def\arraystretch{1.5} \begin{array}{c:c:c} Sample & Sample & Sample \ mean \\ No. & values & (\bar{X}) \\ \hline 1 & 3,4 & 3.5 \\ \hdashline 2 & 3,5 & 4 \\ \hdashline 3 & 3,6 & 4.5 \\ \hdashline 4 & 3,7 & 5 \\ \hdashline 5 & 4,5 & 4.5 \\ \hdashline 6 & 4,6 & 5 \\ \hdashline 7 & 4,7 & 5.5 \\ \hdashline 8 & 5,6 & 5.5 \\ \hdashline 9 & 5,7 & 6 \\ \hdashline 10 & 6,7 & 6.5 \\ \hline \end{array}

3. The sampling distribution of the sample means.


Xˉff(Xˉ)Xˉf(Xˉ)Xˉ2f(Xˉ)7/211/107/2049/40411/108/2064/409/222/1018/20162/40522/1020/20200/4011/222/1022/20242/40611/1012/20144/4013/211/1013/20169/40Total101100/201030/40\def\arraystretch{1.5} \begin{array}{c:c:c:c:c} \bar{X} & f & f(\bar{X}) & \bar{X}f(\bar{X})& \bar{X}^2f(\bar{X}) \\ \hline 7/2 & 1& 1/10 & 7/20 & 49/40 \\ \hdashline 4 & 1 & 1/10 & 8/20 & 64/40 \\ \hdashline 9/2 & 2 & 2/10 & 18/20 & 162/40 \\ \hdashline 5 & 2 & 2/10 & 20/20 & 200/40 \\ \hdashline 11/2 & 2 & 2/10 & 22/20 & 242/40 \\ \hdashline 6 & 1 & 1/10 & 12/20 & 144/40 \\ \hdashline 13/2 & 1& 1/10 & 13/20 & 169/40 \\ \hdashline Total & 10 & 1 & 100/20 & 1030/40 \\ \hline \end{array}

4.


E(Xˉ)=Xˉf(Xˉ)=10020=5E(\bar{X})=\sum\bar{X}f(\bar{X})=\dfrac{100}{20}=5

The mean of the sampling distribution of the sample means is equal to the

the mean of the population.


E(Xˉ)=5=μE(\bar{X})=5=\mu

5.

Var(Xˉ)=Xˉ2f(Xˉ)(Xˉf(Xˉ))2Var(\bar{X})=\sum\bar{X}^2f(\bar{X})-(\sum\bar{X}f(\bar{X}))^2

=103040(10020)2=34=0.75=\dfrac{1030}{40}-(\dfrac{100}{20})^2=\dfrac{3}{4}=0.75

Var(Xˉ)=34=320.8660\sqrt{Var(\bar{X})}=\sqrt{\dfrac{3}{4}}=\dfrac{\sqrt{3}}{2}\approx0.8660

Verification:

Var(Xˉ)=σ2n(NnN1)=22(5251)Var(\bar{X})=\dfrac{\sigma^2}{n}(\dfrac{N-n}{N-1})=\dfrac{2}{2}(\dfrac{5-2}{5-1})

=34=0.75,True=\dfrac{3}{4}=0.75, True


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