Posted by **John** on Monday, November 5, 2012 at 9:53am.

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**, Monday, November 5, 2012 at 6:57pm
Let's look at your data:

n1 = 250

n2 = 215

p1 = 175/250

p2 = 43/215

Formula:

CI99 = (p1 - p2) ± 2.58 √(p1(1-p1)/n1 + p2(1-p2)/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**, Thursday, March 14, 2013 at 5:04pm
.5 ± .103

- Statistics -
**Math Whizz**, Thursday, March 14, 2013 at 5:05pm
.5 } .103, because, as the math guru said the formula is (p1 - p2) } 2.58 ã(p1(1-p1)/n1 + p2(1-p2)/n2), the 2.58 comes from the z-score 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(1-p1)/n1 + p2(1-p2)/n2=.1026887336

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