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Until this year the mean braking distance of a Nikton automobile moving at 60 miles per hour was 175 feet. Nikton engineers have developed what they consider a better braking system. They test the new brake system on a random sample of 64 cars and determine the sample mean braking distance (assume the population standard deviation is known to be 32 feet). How many cars should be tested if Nikton wants to be 95% confident of being within 1 foot of the population mean braking distance?

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Type: Question • Score: 2 • Views: 1,814 • Replies: 7

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Ummm...One hundred? No, wait. Two hundred. Nope? I dunno.

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@amansgh1,

Don't you know that 87 % of all statistics are made up on the spot?

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@amansgh1,

You can use the formula n>2[(Z2asigma)/d]^^2

Z2a = 1.96 from the standard normal distribution for a two-sided test at 95% confidence, d = 1ft, and sigma = 32ft.

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@JPB,

Hey, JPB, translate that into plain English will ya?

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@cicerone imposter,

7868

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@JPB,

Gotcha!

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@JPB,

JPB you shortcutting sexy squirrel, you can do my bullwinkle homework anytime.

z = (sample mean - mu)/(s/root n) where sample mean minus mu is + or - 1 foot
within 1 above the mean is

1.96 = 1 / (32/root n) so

n = (32*1.96)^2 and for 1 below the mean just double 3934

n > 7868

I could have sworn you just said that.

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