Question 324064
A standard placement test has a mean of 115 and a standard deviation of  = 10. Determine the minimum sample size if we want to be 90% certain that we are within 2 points of the true mean.
----
Since E = zs/sqrt(n)
---
sqrt(n) = zs/E
---
So, n = [zs/E]^2
---
z for 90% CI = 1.645
s = 10
E = 2
---
n = [1.645*10/2]^2 = 68 when rounded up
============================================
Cheers,
Stan H.