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Of the 100 bulbs in a box, 5 are defective. If two bulbs are selected

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Of the 100 bulbs in a box, 5 are defective. If two bulbs are selected  [#permalink]

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New post 24 Dec 2018, 01:57
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Question Stats:

70% (01:03) correct 30% (00:59) wrong based on 57 sessions

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Of the 100 bulbs in a box, 5 are defective. If two bulbs are selected at random, what is the probability that both of the bulbs are fine?

(A) (94+95)/(100*99)

(B) (94*95)/(100*99)

(C) 1-(4*5)/(100*99)

(D) (95/100)*(94/100)

(E) (95/100)+(94/100)

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Re: Of the 100 bulbs in a box, 5 are defective. If two bulbs are selected  [#permalink]

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New post 24 Dec 2018, 06:57
The probability of selecting a non-defective light bulb out of 100: (100-5)/100 = 95/100 --- (i)
The probability of selecting a non-defective light bulb out of remaining 99: (100-6/99) = 94/99 --- (ii)

Therefore, multiplying (i) and (ii),
option B) (94*95)/(100*99)
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Re: Of the 100 bulbs in a box, 5 are defective. If two bulbs are selected  [#permalink]

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New post 19 Mar 2019, 04:45
rohan2345 wrote:
Of the 100 bulbs in a box, 5 are defective. If two bulbs are selected at random, what is the probability that both of the bulbs are fine?

(A) (94+95)/(100*99)

(B) (94*95)/(100*99)

(C) 1-(4*5)/(100*99)

(D) (95/100)*(94/100)

(E) (95/100)+(94/100)


Bunuel : If nothing is given, should we consider that we have "non-replacement" case.
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Re: Of the 100 bulbs in a box, 5 are defective. If two bulbs are selected   [#permalink] 19 Mar 2019, 04:45
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Of the 100 bulbs in a box, 5 are defective. If two bulbs are selected

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