Question

1. A random sample of 400 married couples was selected from a large population of married couples. There were 20 couples in which the wife was taller than her husband, and there were 380 couples in which the wife was shorter that her husband. Find a 95 percent confidence interval for the proportion of married couples in the population for which the wife is taller than her husband. Interpret your interval in the context of this question.

Answer 1

`CI = (0.028636,0.071364)`

I am 95% confident that the true proportion of couples where the wife is taller than her husband is captured in the interval (.028, .071)

Explanation:

Given

`n = 400`

`x = 20` --- taller wife

`y = 380` --- shorter wife

Required

Determine the 95% confidence interval of taller wives

First, calculate the proportion of taller wives

`\hat p = (x)/(n)`

`\hat p = (20)/(400)`

`\hat p = 0.05`

The z value for 95% confidence interval is:

`z = 1.96`

The confidence interval is calculated as:

`CI = \hat p \± z \sqrt{(\hat p (1 - \hat p))/(n)}`

`CI = 0.05 \± 1.96* \sqrt{(0.05 (1 - 0.05))/(400)}`

`CI = 0.05 \± 1.96 * \sqrt{(0.0475)/(400)}`

`CI = 0.05 \± 1.96 * √(0.00011875)`

`CI = 0.05 \± 1.96 * 0.01090`

`CI = 0.05 \± 0.021364`

This gives:

`CI = (0.05 - 0.021364,0.05 + 0.021364)`

`CI = (0.028636,0.071364)`