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Old 07-15-2012
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Stats 95% Of the Population

A random sample of 100 12-year-old boys were chosen and the heights of these 100 boys recorded. The sample mean height is 64 inches, and the sample standard deviation is 5 inches. Assuming heights of 12-year-old boys are normally distributed. Which interval below includes approximately 95% of the heights of 12-year-old boys?
a. 63 to 65 inches.
b. 39 to 89 inches.
c. 54 to 74 inches.
d. 59 to 69 inches.
e. Cannot be determined from the information given.
f. Can be determined from the information given, but none of the above choices is correct.
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Old 07-15-2012
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because this is a normal distribution curve ...
mean=median=mode

in such a curve 95% CI is the mean +/- 2 SD

ie 64 +/- 2x5

ie 64+/- 10

so 54--74 ie C
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Old 07-15-2012
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why not A.....using standard error of mean?
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Old 07-16-2012
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Quote:
Originally Posted by stfidel View Post
why not A.....using standard error of mean?
What's that
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Old 07-16-2012
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For interval we use the formula
interval = mean +/- Z(sd/n)
so interval = 64 +/- 2(5/10) {at 95 % ci z = 2)
= 63 or 65
so A
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Old 07-16-2012
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Quote:
Originally Posted by mayursn39 View Post
For interval we use the formula
interval = mean +/- Z(sd/n)
so interval = 64 +/- 2(5/10) {at 95 % ci z = 2)
= 63 or 65
so A
but the question says that it is a normal distribution curve.
so u just use the +/- 2 SD formula for 95% CI
right??
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Old 07-16-2012
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No idea.. I guess you are right .. May be this formula doesnt apply for Normal distribution.. will have to check it.
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Quote:
Originally Posted by tyagee View Post
What's that
at tyagee...i meant the formula used below by others to arrive at the option A...

I have always known wen u are given the sample size population u have to use the said formula...

If not...use Mbbs2010 direct method ...cheers
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