The number of telephone calls N between two cities A and B varies directly as the population P(_{A}), P(_B) respectively and inversely as the square of the distance D between A and B. Which of the following equations represents this relation?
-
A.
N = (frac{kp_A}{D^2} + {cp_B}{D^2}) -
B.
N = (frac{k P_{A} P_{B} }{D^2}) -
C.
N = (frac{kD_AP_D}{B^2}) -
D.
N = (frac{kD^2_AP_D}{B})
Correct Answer: Option B
Explanation
(N propto P_{A}); (N propto P_{B}); (N propto frac{1}{D^{2}})
(therefore N propto frac{P_{A} P_{B}}{D^{2}})
(N = frac{k P_{A} P_{B}}{D^{2}})