Well, tonight I had my first midterm exam at New York University. It was in Econometrics and Applied Statistics. The exam wasn't too bad, but I know I missed a 1-point question about moment-generating functions. It was easier than I had expected. The test had 16 questions worth 1 point each and then 12 questions worth 7 points each. Here is the easiest of the 7 point questions:
You will draw balls without replacement out of a container containing 3 blue and 5 red balls. What is the probability of drawing a red ball on the third draw?
Tuesday, October 10, 2006
Econometrics Midterm
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1 comments:
This question is interesting and I tried to work it out, but felt confused.
1.Suppose the first two times both drew the blue balls, then the probability of drawing a red ball on the third draw should be 3/8*2/7*5/6, right?
2.then I tried to assume that the first two times both drew the red balls, then the probability changed to 5/8*4/7*3/6
3.there are also another two assumptions--draw a blue one first and then a red one, or the opposite way--then the probability would be 3/8*5/7*4/6 or 5/8*3/7*4/6, which are the same
but No.2&3 can get the same answer, while No.1 is different. Why is that? Did I forget to consider something when I made the assumptions?
I am curious to know the answer. Please post it or email me,hehe, thanks;-)
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