a. From the information given here determine the 95% confidence interval estimate of the population mean.
x = 100 = 20 n = 25
b. Repeat part (a) with x = 200.
c. Repeat part (a) with x = 500.
d. Describe what happens to the width of the confidence interval estimate when the sample mean increases.
"\\bar x=100"
"\\sigma =20"
"n =25"
a) Confidence interval is:
"100\\pm Z_{\\frac{1-0.95}{2}}\\frac{20}{\\sqrt{25}}=100\\pm Z_{0.025}\\cdot 4=100\\pm1.96 \\cdot4=100\\pm 7.84"
So given the 95% confidence level the interval is (92.16, 107.84)
b) "\\bar x=200": "200\\pm 7.84"
The 95% confidence interval is (192.16, 207.84)
c) "\\bar x=500": "500\\pm 7.84"
The 95% confidence interval is (492.16, 507.84)
d) As we can see, increasing the sample mean does not change the width of the confidence interval; it only changes where the interval is centered.
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