Question

A random sample of 145 students is chosen from a population of 4250 students. IF the mean IQ in the sample is 130 with a standard deviation of 7, what is the 90% confidence interval for the students IQ score?
A 98.98-101.02
B 109-112
C 125-135
D 129.05-130.95

Answer 1

how many of them have a mean of 130 ....

Answer 2

It doesn't say :/

Answer 3

since A and B dont even contain 130, then cant possibly be it

Answer 4

yea im thinking D, just want to be sure

Answer 5

d might not be quite right

Answer 6

you recall how to find a zscore?

Answer 7

How should i check? without numbers im a big confused how to do it lol

Answer 8

we want to know how many standard deviations fit between the mean, and an end point

Answer 9

\[\frac{endpoint-130}{7}\]

Answer 10

we need to be between 1 and 2 since they represent 65 and 95 percent of the data

Answer 11

.95/7 is less then 1

5/7 seems a better fit, but this is without any real calculations

Answer 12

but a memory is forming .... might have to multiply by the sqrt of the sample size

Answer 13

\[\bar x\pm Z_{.9500}(7/\sqrt{n})=\mu\]

Answer 14

so by 65.19?

Answer 15

not 95% .... 90% which i think has a z of 1.576 or thereabouts

Answer 16

no

130+1.576(7/sqrt(145))

yeah, d is looking better now

Answer 17

alright good, because your equations look alot better than mine do lol

Answer 18

when looking for a mean of a mean we use the sample error which is just a modified version of the standard deviation

Answer 19

Thanks for the help amistre, youre the best man

Answer 20

good luck :)

Answer 21

yeah, d is our choice