probability

Question

Comments

answer is D???

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they have given the answer as A

Answer 1

here is my ANSWER

for the FIFTH CASE WE NEED TO IDENTIFY THE fourth bad tube should be found

so the previous four cases 3 bad tubes and 1 good bulb must be selected so it can be done in 4C3 * 6C1 and these must be arranged as the selection can be BBBG but other cases are also possible like GBBB so number of possible cases will be 4C3 * 6C1*4!/3!*1!=4*4C3 * 6C1

the probability will be 4C3 * 6C1 * 4 / 10C4 in the fifth attempt the fourth bad bulb should come out so probability of that is 1/6

so total probability is 4C3 * 6C1 * 4 / 10C4 * 1/6 = 8/105 is the answer i am getting verify

Comments

Good point @air 1, but placing reaming items is causing no problems bcoz it going to be ^xC_x, so it is only going to multiply by one. Bcoz all good items are identical right.

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Your point is correct as sequence of length 4,5 and so on will be there. But then it is reducing sequences of length 10, and not making any difference in calculation.

So sample space will be ¹⁰C₄

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@rahul its the same. thanks for helping.