1. ## 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?

Its killing me.

2. 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

3. ## Thank you very much

You explained it in two lines. The book is awful.

4. 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.

5. I'd just like to say I agree with everything Mr Fantastic said and promise to be a bit more careful in future.

6. 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