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JAMB Mathematics 1983 Question 6

Question 6

Variation

If x is jointly proportional to the cube of y and the fourth power of z. In what ratio is x increased or decreased when y is halved and z is doubled?

  1. A.4:1 increase
  2. B.2:1 increase
  3. C.1:4 decrease
  4. D.1:1 no change
  5. E.3:4 decrease.
Show the answer and explanation

Answer: B (2:1 increase)

Explanation

x = ky³z⁴. Halving y multiplies x by (½)³ = 1/8 and doubling z multiplies it by 2⁴ = 16, so x is multiplied by 2: an increase in the ratio 2:1.