Posted by miriam on Thursday, March 31, 2011 at 12:40am.
of all 3to 5year old children, 56% are enrolled in school. If a sample of 500 such children is randomly selected, find the probability that at least 250 will be enrolled in school.

statistics  MathGuru, Thursday, March 31, 2011 at 11:21am
Find mean and standard deviation. Use zscores to find z, then a ztable to find your probability based on the zscore. This is a normal approximation to the binomial distribution.
I'll get you started:
mean = np = (500)(.56) = ?
standard deviation = √npq = √(500)(.56)(.44) = ?
Note: q = 1  p
Finish the calculations.
To find zscore:
z = (x  mean)/sd
Note: x = 250
Once you have the zscore, look in a ztable using the score to find your probability. Remember that the question is asking "at least 250" when looking at the table. 
statistics  Anonymous, Wednesday, April 11, 2012 at 4:33pm
.243