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JAMB Mathematics 1978 Question 17

Question 17

Mensuration of Plane Shapes

If a circular paper disc is trimmed in such a way that its circumference is reduced in the ratio 2:5, in what ratio is the surface area reduced?

  1. A.8:125
  2. B.2:5
  3. C.8:25
  4. D.4:25
  5. E.4:10.
Show the answer and explanation

Answer: D (4:25)

Explanation

Circumference is proportional to the radius and area to the radius squared, so the areas are in the ratio 2² : 5² = 4 : 25.