In a large population of adults, the mean IQ is 112 with a standard deviation of 20. Suppose 200 adults are randomly selected for a market research campaign. The probability that the sample mean IQ is greater than 110 is...?

Answer 1

your z score is (110-112)/20 = -.1

if you have a normal distribution table, look up the probability for that score, you should get .4602

that means the the prob. of a score of less than 110 is .4602
so the prob of getting higher than 110 is 1-.4602
= .5398

here is a nice applet that lets you enter your original values, it graphs it and gives you the results

http://davidmlane.com/hyperstat/z_table.html