SOLUTION: A standard placement test has a mean of 125 and a standard deviation of 15. Determine the minimum sample size if we want to be 90% certain that we are within 3 points of the true m

Question 651636: A standard placement test has a mean of 125 and a standard deviation of 15. Determine the minimum sample size if we want to be 90% certain that we are within 3 points of the true mean.
Right now I have Za/2= 1.645 and the margin of error is where I am getting stuck. I have it up to the point of 16.45/sqr root of n=3. I think the next step is to figure out n by n=(16.45/3)^2= 30.06. I don't know where to go from there or if I am finished?
Answer by reviewermath(1029) (Show Source): You can put this solution on YOUR website!
n =
=
= 68 (round up)
Answer:
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