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Sum of two positive numbers are multiplied by each number separately. The products thus obtained are 510 and 390. What is the difference of the two numbers?

A.	2	B.	5
C.	3	D.	4

Answer and Explanation

Answer:4

Explanation:
Let the numbers be x, y.
x(x+y) = 510, y(x+y) = 390
x2 + xy = 510 …… (1)
y2 + xy = 390 …… (2)
Adding (1) and (2)
x2 + xy + xy + y2 = 510 + 390 = 900
(x+y) 2 = 900 = (30) 2
(x+y) = 30
Subtracting (2) from (1)
x2 + xy – xy - y2 = 510 - 390 = 120
x2 - y2 = 120
(x+y) (x-y) = 120
(x-y) = 4.

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