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Question
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
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
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