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Probability

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Probability

by gunjan1208 » Wed Oct 05, 2011 12:38 am
Please help me explaining the answer! Thanks in Advance

For one roll of a certain die, the probability of rolling a two is 1/6. If this die is rolled
4 times, which of the following is the probability that the outcome will be a two at
least 3 times?
(A) (1/6)4
(8) 2(1/6i + (1/6)4
(C) 3{1/6)3(5/6) + (1/6)4
(O) 4{1/6)3{5/6) + (1/6)4
(E) 6{1/6)3{5/6) + (1/6)4
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by sl750 » Wed Oct 05, 2011 1:05 am
Probability of a 2 occurring at least 3 times when the die is rolled 4 times is

4C3(1/6)^3*5/6 + 4C4(1/6)^4

You can use the Bernoulli trials formula too. Which is what I did

(p+q)^4 . p=1/6; q=5/6
4C0*p^4+ 4C1*p*q^3+ 4C2*p^2*q^2 + 4C3*p^3*q + p^4
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by shankar.ashwin » Wed Oct 05, 2011 1:05 am
You have 5 options,

222X
22X2
2X22
X222 and (X could be any No other than 2)

2222

(1/6) (1/6) (1/6) (5/6) * 4 + (1/6)^4.

(1/6)^3 * (5/6) * 4 + (1/6) ^ 4.

Your answer choices dont have powers in them. Could you pls chk?
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