1. ## standard deviation portions

A bakery firm finds that its average weight of the most popular package of cookies is 32.06 ounces with a standard deviation of .1 ounces. what portion of cookie packages will weigh less than 31.9 ounces and more than 32.3 ounces?

2. Originally Posted by jax760
A bakery firm finds that its average weight of the most popular package of cookies is 32.06 ounces with a standard deviation of .1 ounces. what portion of cookie packages will weigh less than 31.9 ounces and more than 32.3 ounces?
First calculate the z-value corresponding to X = 31.9 and X = 32.3. Can you do this?

Then calculate Pr(Z < z-value for X = 31.9) and Pr(Z > z-value for X = 32.3). Can you do this?

Add the above two probabilities together and multiply the result by 100 to get the required portion as a percentage.

3. Thats where my problem is, I have about three formulas I can use to calculte the z and I'm not sure which one I should use, is it bermulia i'm not sure i spelled that right.

4. Originally Posted by jax760
Thats where my problem is, I have about three formulas I can use to calculte the z and I'm not sure which one I should use, is it bermulia i'm not sure i spelled that right.
Whatever you're trying to spell is irrelevant to this question. Unless you're trying to spell $\displaystyle Z = \frac{X - \mu}{\sigma}$.

Now get the z-values. Then calculate the probabilities. (review the section in your class notes or textbook on calculating probabilities using a standard normal distribution if necessary).