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# Confidence Intervals?

Hi please really need help with this question to undestand

Last year, 10,000 people completed the Dublin maraton. You collected the times for the race of a random sample of 256 of them. The average time for the sample is 3hrs and 30mins with a sandard deviation of 48mins. Calculate and comment on the 99%confidence interval for the mean time for all 10,000 maraton runners.

We were doing the question in class using a z test but i don't understand any of it!

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- GuillermoLv 71 decade agoFavorite Answer
Pf(3.5 - 2.575*48/sqrt(256) < μ < 3.5 - 2.575*48/sqrt(256)) = 1 - 0.01

Pf(3.5 - 7.725 < μ < 3.5 + 7.725) = 0.99

Pf( -4.225 < μ < 11.225) = 0.99

Pf ( 0 < 11.225) = 0.99

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