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 the two balls are red?
533
536
103132
3136
Correct answer is A
Total number of balls = 5 + 3 + 4
= 12 balls
P(first ball is red) = 512
P(second ball is red) = 411
∴ P(both balls are red) = \frac{5}{12} \times \frac{4}{11}
= \frac{5}{33}
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