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Question
From a bag containing 10 red, 4 blue and 6 black balls, a ball is drawn at random. Find the probability of drawing a blue or black ball
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Solution
The bag contains 10 red, 4 blue and 6 black balls, i.e., 10 + 4 + 6 = 20 balls.
One ball can be drawn from 20 balls in 20C1 ways.
∴ n(S) = 20C1 = 20
Let event B: The ball drawn is blue or black.
There are 4 blue and 6 black balls.
∴ 1 blue ball can be drawn from 4 blue balls in 4C1 ways or 1 black ball can be drawn from 6 black balls in 6C1 ways.
∴ n(B) = 4C1 + 6C1 = 4 + 6 = 10
∴ P(B) = `("n"("B"))/("n"("S"))`
= `10/20`
= `1/2`.
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