Question

A sample of n=16 values from a normal distribution with known variance sigma = 1 is used to construct a 95% confidence interval for the unkown mean u. What does the width of the confidence interval equal?

Answer 1

unknown*

Answer 2

since sd = sqrt(variance) we have a an sd of 1

Answer 3

within 2 sds of the mean is 95% of the data

Answer 4

the width of the confidence interval is -2 to 2, with the mean being 0

Answer 5

I think we are supposed to use t distribution tables or am i wrong?

Answer 6

it is a simple random sample? :)

Answer 7

with n < 30 the t would be good, i gotta get to clretrice so good luck :)

Answer 8

that's the thing, i don't know how to use t distribution to work it out. the value for t for 16 is 2.12 i think
so 2.12 * 1/4 is 0.53 and that's incorrect

Answer 9

the t distribution table is set up for "degrees of freedom", which in the books tend to be n-1

so find 16-1 = 15 on the left and move over till it lines up with the 2 tails = .05; since the tails are the 5% that is left over from the 95% that is taken up in the interval