Algebra

Quantitative Aptitude (CGL)

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If 5x + 9y = 5 and 125x³ + 729y³ = 120 then the value of the product of x and y is:

135

1/45

1/35

Explanation:

Given,
5x + 9y = 5 .....(i)
125x³ + 729y³ = 120 ....(ii)
Make whole cube of 1st equation, we get
(5x + 9y)³ = (5)³
⇒ 25x³ + 729x³ + 3 × 5x × 9y (5x + 9y) = 125
Put the value of given terms in equation
⇒ 25x³ + 729x³ + 3 × 5x × 9y (5x + 9y) = 125
⇒ 20 + 135xy × 5 = 125
⇒ 135xy × 5 = 5
⇒ xy = 1/135.

By: Amit Kumar

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