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Hi, I'm having trouble with 1b on hw 13. I found the mean and standard deviation, which I got to be 318 and 149.46. 300 and up is a correct poll result, so 318-300=18 and then divided by 149.46=.12 Then I divided that by 2 to get only one side of the mean, I am unsure of what to do next, do I add .5, which is the other half? That didn't make sense becasue that makes about .506 and if I put that in for z on the table that gets an area of less than half, which doesn't make sense.

Peter - I think you need to recheck your standard deviation. It should be the square root of 600 • .53 • .47

When you divide 18 by the s.d. that gives you the z-value. You'll need to use that with the table on p399 to help you find the probability.

When you divide 18 by the s.d. that gives you the z-value. You'll need to use that with the table on p399 to help you find the probability.