Question 1109598: In a survey, 26 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $39 and standard deviation of $5. Construct a confidence interval at a 90% confidence level.
Give your answers to one decimal place._______±_______
AND
If n=350 and p^ (p-hat) =0.26, find the margin of error at a 95% confidence level.
Give your answer to three decimals
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! Given all the assumptions, the interval is a t 0.975, df=25 *5/sqrt(26)
=1.71*5/sqrt(26)
or +/-1.68
(37.3, 40.7)
This is +/- z(0.975)*sqrt(.26*.74/350), or +/- 0.046
check is that for 95% CI the error is roughly 1/sqrt(n), so if n=400, error is 1/20 or 5%.
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