# Statistic Help

• Jan 26th 2008, 02:02 PM
CavalryScout
Statistic Help
The mean is 100. Standard Deviation is 16 on a normal curve.

The question is:
If the distribution of mental ability scores is normal, the middle 68 percent of the scores should lie between what two scores?
answer: 84 to 116. How do you find this?

The next question is:
The middle 96 percent of the mental ability scores should be between what two values?

• Jan 26th 2008, 02:11 PM
a tutor
I think 'they' expect you to just learn these two facts.

68% lie between mean - 1 sd and mean + 1 sd

So you get 100-16 to 100+16

95% lie between mean -2 sd and mean + 2 sd
So you get 100-32 to 100+32
• Jan 26th 2008, 04:23 PM
CavalryScout
Thank you very much
You explained it in two lines. The book is awful.
• Jan 26th 2008, 04:44 PM
mr fantastic
Quote:

Originally Posted by CavalryScout
You explained it in two lines. The book is awful.

Maybe the book used a method that:

1. Gets a more accurate answer, and

2. Provides a template for answering questions like

"If the distribution of mental ability scores is normal, the middle [40] percent of the scores should lie between what two scores?"

You should realise that

"68% lie between mean - 1 sd and mean + 1 sd"

is a rough rule of thumb ("68-95-99.7 rule") - useful under certain circumstances.
• Jan 27th 2008, 06:23 AM
a tutor
I'd just like to say I agree with everything Mr Fantastic said and promise to be a bit more careful in future. :)
• Jan 27th 2008, 01:02 PM
mr fantastic
Quote:

Originally Posted by a tutor
I'd just like to say I agree with everything Mr Fantastic said and promise to be a bit more careful in future. :)

Hey, it's no big deal. Where I was coming from is that sometimes a student gets an easy question that can be done using an easy method (often just a memorised rule), but when the question gets a bit trickier (like the example I gave) the student flounders becuase they have no general process to fall back on.

Great to have you on board, by the way (Handshake)