Multiple choice

In bag A there are 5 red balls, X green balls and 7 yellow balls. Probability of drawing one green ball from bag A is 2/5. In bag B there are (X-3) red balls, (X-4) green balls and 6 yellow balls. 2 balls are drawn from bag B. Find the probability that both the balls are red colour?

  1. 2/23

  2. 3/21

  3. 4/21

  4. 2/21

  5. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Bag A: P(green) = X/(12+X) = 2/5, so 5X = 24 + 2X, giving X = 8. Bag B has (8-3)=5 red, (8-4)=4 green, 6 yellow = 15 total. P(2 red) = (5/15) × (4/14) = 20/210 = 2/21.

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