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A box contains 5 red, 3 green and 4 blue balls. A boy is ...

A box contains 5 red, 3 green and 4 blue balls. A boy is allowed to take away two balls from the box. What is the probability that one is green and the other is blue?

A.

211

B.

512

C.

812

D.

711

Correct answer is A

Total number of balls = 5 + 3 + 4 = 12 balls

P(one ball is green and the other is blue) = P(first ball is green and second blue) + P(first ball is blue and the second green)

 = 312×411+412×311

= 211