Statistics
posted by Tom .
Calculate the following:
a) Determine the sample size necessary to estimate a population mean to within 1 with a 90% confidence given that the population standard deviation is 10.
b) Suppose that the sample was calculated at 150. Estimate the population mean with 90% confidence.

Formula for a):
n = [(zvalue * sd)/E]^2
...where n = sample size, zvalue will be found using a ztable to represent the 90% confidence interval, sd = 10, E = 1, ^2 means squared, and * means to multiply.
Plug the values into the formula and finish the calculation. Round your answer to the next highest whole number.
For b) Use a confidence interval formula:
CI90 = mean + or  zvalue (sd/√n)
I'll let you take it from here. 
10