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JAMB Mathematics 2004 Question 48

Question 48

Probability

Some white balls were put in a basket containing twelve red balls and sixteen black balls. If the probability of picking a white ball from the basket is 3/7, how many white balls were introduced?

  1. A.32
  2. B.28
  3. C.21
  4. D.12
Show the answer and explanation

Answer: C (21)

Explanation

x/(28 + x) = 3/7 gives 7x = 84 + 3x, so x = 21.