A random sample of 130 students is chosen from a population of 4,500 students. If the mean IQ in the sample is 120 with a standard deviation of 5, what is the 99% confidence interval for the students' mean IQ score?

Question

anonymous · Answer

@calculusxy

amistre64 · Answer

your sample data will have to be adjust most likely

sd*sqrt(n)

amistre64 · Answer

divide not * ...

anonymous · Answer

i dont understand

amistre64 · Answer

do you recall a zscore formula?  might be called a standard score

anonymous · Answer

no i have never heard of that

amistre64 · Answer

maybe you recall the look of it ...$$z=\frac{x-\bar x}{\sigma}$$
??

anonymous · Answer

no but i can try it

anonymous · Answer

can u help me dumbcow?

anonymous · Answer

i really dont understand that formula

amistre64 · Answer

its one of the most basic formulas in stats.  something that you would have most likely been exposed to way before the content of this question.

amistre64 · Answer

http://www.wikihow.com/Calculate-Confidence-Interval

anonymous · Answer

so its (.99 x 5) + 120?

anonymous · Answer

@amistre64

amistre64 · Answer

we take the sample mean as the midpoint of the interval and adjust the z score as needed to cover the spread, let me get a better view of it

amistre64 · Answer

a 99% interval means we want 1/2 % for tails ..

amistre64 · Answer

what is a zscore for 1/2%?  then times that by o~/sqrtn

amistre64 · Answer

i think the z score is +- 2.576 if memory serves

amistre64 · Answer

so the interval itself would be:  sample mean +- 2.576(5/sqrt(130))

anonymous · Answer

thats -1.129650729

amistre64 · Answer

i agree ... so out interval turns out to be:$$120\pm1.1296...$$
how ever accurate you want to make the decimlas i spose unless they give you a cutoff for it

anonymous · Answer

118.8703493

anonymous · Answer

that is right! thank u so much

amistre64 · Answer

some catches may be that they want a tscore, instead of the z score .. which is harder to determine in my view

amistre64 · Answer

yay!!