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BDF = the binomial distribution probability;
p = the individual probability of the phenomenon (p = 0.5 to get heads in coin tossing);
M = the exact number of successes
N = the number of trials

Thx!

Last edited by Nsentra on 08 Aug 2006, 16:55, edited 1 time in total.

I have the same problem! How in the heck are you going to right it all out on exam day without wasting 2-3 minutes on a problem?
I have never seen it asked like that on GMAT prep..
so I wouldln't worry too too much..

I have the same problem! How in the heck are you going to right it all out on exam day without wasting 2-3 minutes on a problem? I have never seen it asked like that on GMAT prep.. so I wouldln't worry too too much..

I appreciate Kaplan for putting some stuff for me in baby terms, but sometimes by not explaining everything behind the answer they are preventing me from seeing the real math behind the solution

Exactly, nissan! I was working too quickly (trying to fit in those 2 minutes!) and accidently skipped one case...

Anyway, you don't have to write down all possible combinations of heads and tails.

You just need to remember that 2^4 is total number of combinations (=16)
and then count only those cases where we have eaither 4 heads (1 such case) or 3 heads (4 cases). So,

Exactly, nissan! I was working too quickly (trying to fit in those 2 minutes!) and accidently skipped one case...

I know for a fact that is what is going to happen to me on a test. Thanks for giving another thought on how to do this though.

Cheer up! That's exactly why you are here, isn't it. A little bit of practicing and you will get confident enough so that none of the tricks GMAT trows at you would make you blink...