# Thread: Homework help (the empirical rule)??

1. ## Homework help (the empirical rule)??

Hello,
Can anyone help me with this problem?

SAT math scores have a bell shaped distribution with a mean of 515 and a standard deviation of 114.

a) what percentage of scores are between 401 and 629?
b) what percentage of scores are less than 401 or greater than 629?\
c) and what percentage of scoresare greater than 743?

I have read this section in my book and I am so confused.
Thank you so much, anyone who may help!!

2. ## Re: Homework help (the empirical rule)??

Calculate the z score. The well-known formula is z = (score - mean) / (standard deviation). Then use the standard normal table.

Example.
P(score above 629) = ?
First, z = (629 - 515) / 114 = 1.
Second, look at the standard normal table, something like http://www.sjsu.edu/faculty/gerstman...fo/z-table.htm: the table tells me that P(z<1)=.5398.
Lastly, some straightforward logic: we wanted score above, so we want to find P(z>1). It is 1 - .5398.

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