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 December 18th, 2009, 08:03 PM #1 Newbie   Joined: Dec 2009 Posts: 1 Thanks: 0 probabilities! i'm a first-time poster.. need some help on this one question i need to figure out to study for a final coming up ******** at a high school prom, the probability of exactly 15 out of 70 students that will wear all-white attire (tuxedos, gowns, etc.) is about 0.2698. What is the probability of a randomly selected student that is wearing all-white attire? ******** so for this question, do I use the formula: P= nCx (P^x) (q^n-x) ? If yes, will the data i need to plug into it be: n = 70 x = 15 p = 0.2698 q = 0.7302 ? i'm asking this because the last part threw me off a bit - the probability of a randomly selected student wearing all-white attire. what do I have to do to change my data points if I'm wrong? would n = 15 and x = 1 ???
 December 18th, 2009, 10:03 PM #2 Senior Member   Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3 Re: probabilities! ${70\choose 15}p^{15}(1-p)^{55}= 0.2698$ but I don't see any real solution. The maximum value of the left-hand side is 0.11552573 for p = 0.2142857.
 December 19th, 2009, 03:57 AM #3 Senior Member   Joined: Dec 2009 From: Las Vegas Posts: 209 Thanks: 0 Re: probabilities! Hi all; I am having the same problem : ${70 \choose 15} p^{15}(1-p)^{55}$ Has a maximum at 3 / 14 of .1155257 so their is no way any p can ever equal .2698. Are the numbers correct?

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