Some help on those AP problems...

I don't know about losing one hour of sleep today....stupid clock changes.

I just sent an email response to a good question, relating to problems 1c and number 2; figured I'd throw that bad boy up here for anyone in need.

Alright, let's see how well we can figure this out via email...

First off, letter C...so here's the scenario--someone comes in to have their blood tested. What can happen? The test can be positive or negative. If it's positive, then the person will undergo two more tests; if one of these two tests is positive, the blood sample will receive more expensive and accurate testing.

So our job is to translate this situation to "And" and "Or." So the first sample has to be positive; then, we can have a few situations.

If the first test is negative, there's no more testing involved so we don't care about this situation.

POSITIVE and NEGATIVE and POSITIVE--What happens?
POSITIVE and NEGATIVE and NEGATIVE
POSITIVE and POSITIVE -- Remember, once one of the additional two tests is positive, we're onto the more expensive stuff. So the third won't matter in this case.

Now you just need to find the probability we have a positive or negative test based on all of the information given, and decide which of the scenarios above answer our question.

Onto number 2:

This question first asks about expected value and variance when combining random variables. This is chapter 16 in our book, and there's an example on page 377 which is similar to this, but instead of "M - W" the book is an example of addition.

For (a), you should be able to figure out how to find the expected value and standard deviation after looking at the example. Part (b) asks you to use a Normal approximation based on your answers to (a) to find a probability, so you'll need z-scores (you got that!). The trick is to think--if the woman is taller than the mean, what "kinds" of answers would we get by doing M - W? Then, find the probability of the answer to that question.

I hope this helped...good luck!