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JAMB Mathematics 2008 Question 15

Question 15

Variation

If x − 3 is directly proportional to the square of y and x = 5 when y = 2, find x when y = 6.

  1. A.30
  2. B.21
  3. C.16
  4. D.12
Show the answer and explanation

Answer: B (21)

Explanation

x − 3 = ky2: 2 = 4k, so k = ½. When y = 6, x − 3 = 18 and x = 21.