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JAMB Mathematics 1978 Question 8

Question 8

Variation

The number of telephone calls N between two cities A and B varies directly as the population PA, PB in A and B respectively and inversely as the square of the distance D between A and B. Which of the following equations represents this relation?

  1. A.N = KPA/D2 + CPB/D2
  2. B.N = KPAPB/D2
  3. C.N = KDPAPB
  4. D.N = KDPA + CDPB
  5. E.N = KD2PAPB
Show the answer and explanation

Answer: B (N = KPAPB/D2)

Explanation

Varying directly as both populations puts PAPB on top, and inversely as the square of the distance puts D² underneath, with one constant K.