Multiple choice

In a bag which contains 40 balls, there are 18 red balls and some green and blue balls. If two balls are picked up from the bag without replacement, then the probability of the first ball being red and second being green is 3/26. Find the number of blue balls in the bag.

  1. 12

  2. 10

  3. 18

  4. None of these

  5. Can’t be determined
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let green balls = g. Probability first red then green = (18/40) * (g/39) = 3g/260. Given this equals 3/26, so g = 10. Total balls = 40, so blue = 40 - 18 - 10 = 12. Answer A is correct.

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