Posted by Ashley on Thursday, June 30, 2011 at 2:13pm.
The proportion of baby boys born in the United States has historically been 0.512. You choose an SRS of 55 newborn babies and find that 47% are boys. Do ALL calculations to 5 decimal places before rounding.
(d) In a random sample of 55 newborn babies, what is the probability that 47% of the sample are boys. (Use 3 decimal places). Hint: you are asked to find P( < .47 ). To calculate this first find the zscore and then look up the answer in the Z table.

statistics  MathGuru, Thursday, June 30, 2011 at 5:40pm
Formula for zscore:
z = (x  mean)/sd
Find mean:
mean = np = (55)(0.512) = ?
Find standard deviation:
sd = √npq = √(55)(0.512)(0.488) = ?
Note: q = 1  p
Finish both calculations.
Substitute mean and standard deviation into the zformula. Use 25.85 for x (0.47 * 55 = 25.85).
Once you have the zscore, use the ztable to determine your probability.
I hope this will help get you started. 
statistics  Ashley, Thursday, June 30, 2011 at 8:32pm
Thank you sooo much!! Also thanks for posting steps and not just an answer.