Posted by **Jim** on Tuesday, April 12, 2011 at 10:27pm.

A popular online retailer sells a wide variety of products including books. The proportion of customers that order only books is 21%. If a random sample of 600 customers is taken, what is the probability that more than 24% order only books?

- statistics -
**MathGuru**, Thursday, April 14, 2011 at 6:31pm
Use the normal approximation to the binomial distribution.

First find mean and standard deviation.

mean = np = (600)(.21) = ?

standard deviation = √npq = √(600)(.21)(.79) = ?

Note: q = 1 - p

I'll let you finish the calculations.

Next take .24 times 600. Use that value for x in the z-score equation:

z = (x - mean)/sd

Once you calculate the z-score, look at a z-table to determine the probability. Remember that the problem is asking "more than" when you check the table.

I hope this will help get you started.

- statistics -
**sean**, Monday, November 12, 2012 at 7:57pm
0.983

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