N = 8
Mean = 2.10
stDev = 0.537

What size sample is required to construct a 95% confidence interval with a margin of error of 0.3?
try n = 12, t(.975) with 11 deg. of freedom = 2.2001
so n = ( (.537* 2.2001) / (.3))^2 = 15.5

try n = 14, i get n = 14.95
n = 15, n = 14.74
Why is this a trial and error?
What I don't get is what are we trying to get n to equal?

the answer: n must be between 14 and 15 so, use n = 15.

Question

N = 8
Mean = 2.10
stDev = 0.537

What size sample is required to construct a 95% confidence interval with a margin of error of 0.3?
try n = 12, t(.975) with 11 deg. of freedom = 2.2001
so n = ( (.537* 2.2001) / (.3))^2 = 15.5

try n = 14, i get n = 14.95
n = 15, n = 14.74
Why is this a trial and error?
What I don't get is what are we trying to get n to equal?

the answer: n must be between 14 and 15 so, use n = 15.

anonymous · Answer

This is a good source to use: http://highered.mcgraw-hill.com/sites/dl/free/0072549076/79745/ch07.pdf