1. Mean
μ = 3 + 4 + 5 + 6 + 7 5 = 5 \mu=\dfrac{3+4+5+6+7}{5}=5 μ = 5 3 + 4 + 5 + 6 + 7 = 5 Variance
σ 2 = 1 5 ( ( 3 − 5 ) 2 + ( 4 − 5 ) 2 + ( 5 − 5 ) 2 \sigma^2=\dfrac{1}{5}\big((3-5)^2+(4-5)^2+(5-5)^2 σ 2 = 5 1 ( ( 3 − 5 ) 2 + ( 4 − 5 ) 2 + ( 5 − 5 ) 2
( 6 − 5 ) 2 + ( 7 − 5 ) 2 ) = 2 (6-5)^2+(7-5)^2\big)=2 ( 6 − 5 ) 2 + ( 7 − 5 ) 2 ) = 2
Standard deviation
σ = σ 2 = 2 ≈ 1.4142 \sigma=\sqrt{\sigma^2}=\sqrt{2}\approx1.4142 σ = σ 2 = 2 ≈ 1.4142
2. We have population values 3 , 4 , 5 , 6 , 7 , 3,4,5,6,7, 3 , 4 , 5 , 6 , 7 , population size N = 5 N=5 N = 5 and sample size n = 2. n=2. n = 2. Thus, the number of possible samples which can be drawn without replacement is
( N n ) = ( 5 2 ) = 10 \dbinom{N}{n}=\dbinom{5}{2}=10 ( n N ) = ( 2 5 ) = 10 S a m p l e S a m p l e S a m p l e m e a n N o . v a l u e s ( X ˉ ) 1 3 , 4 3.5 2 3 , 5 4 3 3 , 6 4.5 4 3 , 7 5 5 4 , 5 4.5 6 4 , 6 5 7 4 , 7 5.5 8 5 , 6 5.5 9 5 , 7 6 10 6 , 7 6.5 \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} S am pl e N o . 1 2 3 4 5 6 7 8 9 10 S am pl e v a l u es 3 , 4 3 , 5 3 , 6 3 , 7 4 , 5 4 , 6 4 , 7 5 , 6 5 , 7 6 , 7 S am pl e m e an ( X ˉ ) 3.5 4 4.5 5 4.5 5 5.5 5.5 6 6.5
3. The sampling distribution of the sample means.
X ˉ f f ( X ˉ ) X ˉ f ( X ˉ ) X ˉ 2 f ( X ˉ ) 7 / 2 1 1 / 10 7 / 20 49 / 40 4 1 1 / 10 8 / 20 64 / 40 9 / 2 2 2 / 10 18 / 20 162 / 40 5 2 2 / 10 20 / 20 200 / 40 11 / 2 2 2 / 10 22 / 20 242 / 40 6 1 1 / 10 12 / 20 144 / 40 13 / 2 1 1 / 10 13 / 20 169 / 40 T o t a l 10 1 100 / 20 1030 / 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} X ˉ 7/2 4 9/2 5 11/2 6 13/2 T o t a l f 1 1 2 2 2 1 1 10 f ( X ˉ ) 1/10 1/10 2/10 2/10 2/10 1/10 1/10 1 X ˉ f ( X ˉ ) 7/20 8/20 18/20 20/20 22/20 12/20 13/20 100/20 X ˉ 2 f ( X ˉ ) 49/40 64/40 162/40 200/40 242/40 144/40 169/40 1030/40
4.
E ( X ˉ ) = ∑ X ˉ f ( X ˉ ) = 100 20 = 5 E(\bar{X})=\sum\bar{X}f(\bar{X})=\dfrac{100}{20}=5 E ( X ˉ ) = ∑ X ˉ f ( X ˉ ) = 20 100 = 5 The mean of the sampling distribution of the sample means is equal to the
the mean of the population.
E ( X ˉ ) = 5 = μ E(\bar{X})=5=\mu E ( X ˉ ) = 5 = μ
5.
V a r ( X ˉ ) = ∑ X ˉ 2 f ( X ˉ ) − ( ∑ X ˉ f ( X ˉ ) ) 2 Var(\bar{X})=\sum\bar{X}^2f(\bar{X})-(\sum\bar{X}f(\bar{X}))^2 Va r ( X ˉ ) = ∑ X ˉ 2 f ( X ˉ ) − ( ∑ X ˉ f ( X ˉ ) ) 2
= 1030 40 − ( 100 20 ) 2 = 3 4 = 0.75 =\dfrac{1030}{40}-(\dfrac{100}{20})^2=\dfrac{3}{4}=0.75 = 40 1030 − ( 20 100 ) 2 = 4 3 = 0.75
V a r ( X ˉ ) = 3 4 = 3 2 ≈ 0.8660 \sqrt{Var(\bar{X})}=\sqrt{\dfrac{3}{4}}=\dfrac{\sqrt{3}}{2}\approx0.8660 Va r ( X ˉ ) = 4 3 = 2 3 ≈ 0.8660
Verification:
V a r ( X ˉ ) = σ 2 n ( N − n N − 1 ) = 2 2 ( 5 − 2 5 − 1 ) Var(\bar{X})=\dfrac{\sigma^2}{n}(\dfrac{N-n}{N-1})=\dfrac{2}{2}(\dfrac{5-2}{5-1}) Va r ( X ˉ ) = n σ 2 ( N − 1 N − n ) = 2 2 ( 5 − 1 5 − 2 )
= 3 4 = 0.75 , T r u e =\dfrac{3}{4}=0.75, True = 4 3 = 0.75 , T r u e
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