Statistics
posted by John .
A random sample of 250 men yielded 175 who said they'd ridden a motorcycle at some time in their lives, while a similar sample of 215 women yielded only 43 that had done so. Find a 99% confidence interval for the difference between the proportions of men and women who have ridden motorcycles.
.4688 ± .085
.5 ± .112
.5 ± .103
.5 ± .085
.5 ± .078

Statistics 
MathGuru
Let's look at your data:
n1 = 250
n2 = 215
p1 = 175/250
p2 = 43/215
Formula:
CI99 = (p1  p2) ± 2.58 √(p1(1p1)/n1 + p2(1p2)/n2)
Substitute the values into the formula and calculate. (Convert all fractions to decimals.)
You should be able to select your answer once you have determined the interval. 
Statistics 
Math Whizz
.5 ± .103

Statistics 
Math Whizz
.5 } .103, because, as the math guru said the formula is (p1  p2) } 2.58 ã(p1(1p1)/n1 + p2(1p2)/n2), the 2.58 comes from the zscore table. The question doesn't want you to solve the whole formula, just the first and last.. (175/250)(43/215)=.5 and the ã(p1(1p1)/n1 + p2(1p2)/n2=.1026887336
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