Percentiles, given a mean of 800 and a stand. dev. of 20

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camcascod

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Mar 12, 2007
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Assume certain standardized test scores are approximately normally distributed with a mean of 800 and a standard deviation of 20. Find the following percentiles:

50th: I came up with 800.

95th: I came up with 833 by taking 1.65=x-800/20.

25th: I came up with 786.6 by taking -.67=x-800/20.

Do these look right to you?
 
camcascod said:
95th: I came up with 833 by taking 1.65=x-800/20.
25th: I came up with 786.6 by taking -.67=x-800/20.
Click to expand...
Just fix your notation. These are NOT the same:

x-800/20

(x-800)/20

You tell me why they are different.
 
Why?

There are different, because the one with parantheses is taking x-800 and then dividing it by twenty, and the one with parantheses is subtracting 800 divided by 20 from X.
 
You have to write it before it is fixed.

Your calculations look okay. 786.6 might be a little high, but I don't know your rounding rules.

Good work.
 
Thanks!

Thanks for helping me. I was wondering if there was a way to write equations the way they look in the forum?
 
camcascod said:
I was wondering if there was a way to write equations the way they look in the forum?
Click to expand...
To learn how to use LaTeX, follow any of the links in the "Forum Help" pull-down menu at the very top of each forum page, look at a "quote" of posts containing LaTeX, or (in at least some browsers) put the cursor over the LaTeX and wait for a display of the coding.

Thank you.

Eliz.
 
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