Posted by **Terra ** on Thursday, January 12, 2012 at 5:30pm.

The level of nitrogen oxides (NOX) in the exhaust of a particular car model varies with mean 0.9 grams per mile and standard deviation 0.15 grams per mile .

(a) What sample size is needed so that the standard deviation of the sampling distribution is 0.01 grams per mile ?

- Statistics -
**Terra **, Thursday, January 12, 2012 at 8:14pm
Never mind, got it. If anyone wants to know how to get it though...

1.5/(sq root of .9)=.01

Solve the equation, then square each side.

Answer=225

- Statistics -
**Terra **, Thursday, January 12, 2012 at 8:16pm
And by .9 I definitely meant n.....haha

- Statistics -
**Anonymous**, Wednesday, November 11, 2015 at 9:45am
That is a brutal solution lol

- Statistics -
**Anonymous**, Friday, December 11, 2015 at 8:29pm
Solve what equation? You didn't post an associated equation. and 1.5/sqrt of 0.9 does not equal .01

Then square what? Elaborate please.

- Statistics -
**Hannah**, Monday, October 17, 2016 at 12:59am
Long form:

start with:

0.15 / (square root of n) = 0.01

multiply both sides by (square root of n) which gives you:

0.15 = (0.01) x (square root of n)

divide both sides by 0.01 which gives you:

0.15 / 0.01 = square root of n

both sides to the power of 2:

(0.15 / 0.01)^2 = (square root of n)^2

0.0225 / 0.0001= n

n = 225

Short form:

n = (0.15)^2 / (0.01)^2

n = 0.0225 / 0.0001

n = 225

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