George flips an unfair coin 7 times. The coin has a 1/4 probability of coming up heads and a 3/4 probability of coming up tails. What is the probability that he flips exactly 2 tails?
p = nCr(7,2)*(3/4)2*(1/4)(7-2) → 0.01154
Note: nCr(7,2) = 7!/(2!*5!) = 7*6/2 = 21
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Thanks!
(Which by the way is 189/16384)
+556 
