# Thread: A Normal Distribution Problem

1. ## A Normal Distribution Problem

Okay, I'm not sure wether this is Basic or Advanced, but I am having trouble processing how to find the area in a standard normal distribuution.

Here is the textbook's basic example; the mean is zero, the standard deviation is one, and the z-score is .75. I understand that the equation is Z=(X-mean)divided by standard deviation, and that the back of the book says the answer is .7734, but I don't understand what I must put in the calculator to make this data into that answer.

Also, what if I knew the area, but not the z-score? What would I do then?

EDIT: Oh DUH, forgot. The area before the z-score.

2. Originally Posted by starkWonder
Okay, I'm not sure wether this is Basic or Advanced, but I am having trouble processing how to find the area in a standard normal distribuution.

Here is the textbook's basic example; the mean is zero, the standard deviation is one, and the z-score is .75. I understand that the equation is Z=(X-mean)divided by standard deviation, and that the back of the book says the answer is .7734, but I don't understand what I must put in the calculator to make this data into that answer.

Also, what if I knew the area, but not the z-score? What would I do then?
Look up .75 in a table of the cumulative normal distribution-- there is probably one in your book. If you knew the area but not Z, you would reverse this process.

It's possible that your calculator may have a function that will do this for you, but most simple calculators do not.

3. The table was in the back cover, and it indeed says the intersection between .7 and .05 is .7734. Now I just feel foolish for not thinking of that. Thank you for the shockingly fast late-night reply, awkward.

...Incidentally, would a mean besides zero or a standard deviation besides one require a totally different process? I'm figuring yes, but drawing a blank as to what the equation would look like.

4. If you have something other than a mean of zero and a standard deviation of 1, you convert it to an equivalent "Z-score" by the formula you quoted earlier, Z = (X - mean) / (standard deviation). Z has a normal distribution with mean zero and standard deviation 1, so you can use your table.