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WAEC Mathematics 2008 Question 31

Question 31

Variation

If x ∝ (45 + ½y), which of the following is true?

  1. A.x varies directly as y
  2. B.x varies inversely as y
  3. C.x is partly constant and partly varies as y
  4. D.x varies jointly as 45 and directly as y
Show the answer and explanation

Answer: C (x is partly constant and partly varies as y)

Explanation

x = k(45 + ½y) = 45k + (k/2)y: a constant part plus a part that varies with y, i.e. partial variation.