20
A bag contains X red balls and 5 green balls. 2 balls are picked up from the bag at random, one after the other, without replacement, the probability of both balls being red is 3/7. What will be the value of X?
- A10
- B15
- C13
- D20
Answer not set
Discussion 1
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0
CCommunity
Number of Green Balls = 5
Number of Red balls = X
⇒ Total number of balls = 5 + X
Probability of both balls being red = 3/7
⇒ XC2 / 5 + XC2 = 3/7
Only 10 satisfies the value of X
∴ Number of red balls, X = 10
Number of Red balls = X
⇒ Total number of balls = 5 + X
Probability of both balls being red = 3/7
⇒ XC2 / 5 + XC2 = 3/7
Only 10 satisfies the value of X
∴ Number of red balls, X = 10