# Thread: Determine Mean and Standard Deviation from Z-Score

1. ## Explaining the Percentile Score of Normal Distribution

The instructor announces that 75 percent of students scored above the mean. How do you reconcile this with the fact that, in a normal distribution, half the scores should fall below the mean and half of the scores should fall above the mean?

2. ## Re: Determine Mean and Standard Deviation from Z-Score

Your name isn't a palindrome. How do you reconcile this with the fact that if your name was just "bob" that your name would be a palindrome?

3. ## The Following User Says Thank You to Dason For This Useful Post:

bruin (10-19-2014)

4. ## Re: Explaining the Percentile Score of Normal Distribution

Sounds like it wasn't a normal distribution. Sounds like it was left-skewed.

Yes, many distributions of grades follow a roughly normal distribution, but they certainly don't have to. A left-skewed distribution hints to me that it was an easy test (therefore most people did really well, and there was probably even a ceiling effect) but no matter how easy a test is there are always a handful of students who refuse to study (and therefore bomb it).

5. ## Re: Determine Mean and Standard Deviation from Z-Score

I had to create it in order to see it.

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