Practicing Success

Target Exam

CUET

Subject

General Test

Chapter

Quantitative Reasoning

Topic

Algebra

Question:

If $x+y=2$ and $\frac{1}{x}+\frac{1}{y}=\frac{18}{5}$, then the value of $\left(x^3+y^3\right)$ is:

Options:

$4 \frac{2}{3}$

$4 \frac{3}{5}$

$3 \frac{1}{5}$

$3 \frac{1}{3}$

Correct Answer:

$4 \frac{2}{3}$

Explanation:

If $x+y=2$ 

$\frac{1}{x}+\frac{1}{y}=\frac{18}{5}$

$\frac{x + y}{xy}=\frac{18}{5}$

$\frac{2}{xy}=\frac{18}{5}$

xy = $\frac{5}{9}$

The value of $\left(x^3+y^3\right)$ = 

If x + y  = n

then, $x^3 + y^3$ = n3 - 3 × n × xy

$x^3 + y^3$ = 23 - 3 × 2 × $\frac{5}{9}$

= $x^3 + y^3$ = 8 - $\frac{10}{3}$

$x^3 + y^3$ = $4 \frac{2}{3}$