7-4 page 339 number 17

7-4 page 339 number 17 (link to answer)

Margin of Error Formula for estimating a mean Use confidence intervals to compare the mean birth weight of babies born to mothers who did not use cocaine to the mean birth weight of babies born to mothers who did use cocaine. Use the formulas on page 331 to find the margin of error, Eand the confidence interval for μ

n = 186 s = 696 grams = 3,103 grams

95% confidence level

Margin of Error equals 1.57

3,103 - 100.6 < μ < 3,103 + 100.6

3,002 < μ < 3,204 (no cocaine use)

2,608 < μ < 2,792 (cocaine use from page 337)

The mean birth weight for babies born to mother's who did not use cocaine is between 3,002 and 3,204 grams at the 95% confidence level.

Cocaine use appears to affect birth weight.

Be sure to learn how to look up critical values of t. Table A-3 directions below.

Refer to pages 331 and 332 to learn how to lookup the critical value of t. Once learned, use the following shortcut.

Compute the degrees of freedom: df = n - 1

df = 186 - 1 = 185

Confidence level = 95%

α = 100% - 95% = 5% = 0.05

Look in column "Area in two tails, α = 0.05" and row "df = 185" to find t = 1.984 (for df = 100) or t = 1.972 (for df = 200)

Because 185 is much closer to 200 than 100 choose t = 1.972

STATDISK Instructions