Question

10 defective bulbs are mixed with 90 good ones. One bulb is drawn at random . What is the probability that it is a good one.. tell me fast ​

Answer 1

Answer:

Prob of drawing a good bulp at first draw is 7/10. If we draw a good one, then 6 good bulbs are left in the box out of 9. Then, Prob(both good) = 7/10 × 6/9 = 42/90

In the second case (one good, one faulty) there are 2 alternatives.

First draw good, second faulty : 7/10 × 3/9 = 21/90

First draw faulty, second good: 3/10 × 7/9 = 21/90

Prob of union of these two alternative cases is their sum (they are independent)

21/90 + 21/90 = 42/90

Another way is first finding prob of both faulty and subtract this and p(both good) from 1.

P(both good) + P(both faulty) + P(one good, one faulty) = 1

P(both faulty) = 3/10 × 2/9 = 6/90

Then, P(one good, one faulty) = 1 - 42/90 - 6/90 = 42/90

Answer 2

Answer:

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