Sum

In a box there are 20 non-defective and some defective bulbs. If the probability that a bulb selected at random from the box found to be defective is `3/8` then, find the number of defective bulbs

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#### Solution

Let the number of defective bulbs be “x”

Sample space (S) = 20 + x

n(S) = 20 + x

Let A be the event of getting to be defective

n(A) = x

P(A) = `("n"("A"))/("n"("S"))`

⇒ `3/8 = x/(20 + x)`

⇒ 8x = 3(20 + x) = (60 + 3x)

⇒ 8x – 3x = 60

⇒ 5x = 60

⇒ x = `60/5`

⇒ x = 12

Number of defective bulbs = 12

Concept: Probability

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