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

[camcascod]

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?

 

[tkhunny]

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.

Just fix your notation. These are NOT the same:

x-800/20

(x-800)/20

You tell me why they are different.

 

[camcascod]

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.

 

[camcascod]

Solutions

So, if I fixed my notation would the solutions be correct?

 

[tkhunny]

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.

 

[camcascod]

Thanks!

Thanks for helping me. I was wondering if there was a way to write equations the way they look in the forum?

 

[stapel]

I was wondering if there was a way to write equations the way they look in the forum?

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.