Thread: Help w/Statistics Homework Please :(

These questions are giving me a hard time. Any help is appreciated. Thanks!!

1: The weight of corn chips dispensed into a 48 ounce bag by the dispensing machine has been identified as possessing a normal distribution with a mean of 48.5 ounces and a standard deviation of 0.2 ounces. What proportion of the 48 ounce bags contains more than the advertised 48 ounces of chips?

2: Before a new phone system was installed, the amount a company spent on personal calls followed a normal distribution with an average of $900 per month and a standard deviation of $50 per month. Refer to such expenses as PCE'S (personal call expenses). Using the distribution above, what is the probability that during a randomly selected month PCE'S were between $775.00 and $990.00?

3: Farmers often sell fruits and vegetables at roadside stands during the summer. One such roadside stand has daily demand for tomatoes that is approximately normal distributed with a mean of 134 tomatoes and a standard deviation of 30 tomatoes. How many tomatoes must be available on any given day so that there is only a 1.5% chance that all tomatoes will be sold?

4: Transportation officials tells us that 70% of drivers wear seat belts while driving. Find the probability that more than 579 drivers in a sample of 800 drivers wear seat belts. Hint: This is binomial distribution. Use normal distribution approximations.

Help comes in the form of some questions...

Were there some that did NOT give you problems? It woudl be good to see what sorts of things your can understand well. This will provide a foundation for moving on.

You will HAVE to calculate a Z-Score. This is an unavoidable skill. Your calculator may do it for you. Can you do it?

Question number one i'm pretty sure i did right:
P(x>48) = P(z>(48.5-48/2) = P(z>2.5) = .9938
Double checked w/TI83 normalcdf(48,E99,48.5,0.2) = .9938

I understand a lot of these problems, but these four are the ones giving me a hard time. I have always had trouble with word problems. If the problem is set up for me i.e. mu=48.5 SD= 0.2 P(x>48) i would be fine.

Originally Posted by Fijilight08

Question number one i'm pretty sure i did right:
P(x>48) = P(z>(48.5-48/2) = P(z>2.5) = .9938

There is quite a bit wrong with this. You should take more time with your notation and write what you mean.

P(x>48) -- This is fine.
P(z>(48.5-48/2) -- This is not fine. You have overlooked your algebra. There is a reason you studied the "Order of Operations". Your subtraction is in the wrong order and you have a typo. It should be this:

P(z>((48-48.5)/0.2)

P(z>2.5) - This is obviously wrong. How can the value be greater than zero when the value of interest is below the mean? It should be this:

P(z>-2.5)

P(z>2.5) = .9938 -- This is also very obviously wrong. p(z>2.5) should be a very small number. How did you get almost 1? I think it obvious that you understood what you were writing, you just didn't share it with the rest of us.

Please be careful with the notation.

I understand a lot of these problems, but these four are the ones giving me a hard time. I have always had trouble with word problems. If the problem is set up for me i.e. mu=48.5 SD= 0.2 P(x>48) i would be fine.

As far as setting up the problems and doing fine if someone sets them up for you...well...setting them up is the interesting part that you should be learning. Work on that skill. You'll get it.