If $(0.4x+\frac{1}{x}) = 5$, what is the

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Target Exam

CUET

Subject

General Test

Chapter

Quantitative Reasoning

Topic

Algebra

Question:

If $(0.4x+\frac{1}{x}) = 5$, what is the value of $(0.064x^3+\frac{1}{x^3})$?

Options:

125

110

119

105

Correct Answer:

119

Explanation:

If x + $\frac{1}{x}$ = n

then, $x^3 +\frac{1}{x^3}$ = n³ - 3 × n

If $(0.4x+\frac{1}{x}) = 5$

then, $(0.064x^3+\frac{1}{x^3})$ = 5³ - 3 × 0.4 × 5

$(0.064x^3+\frac{1}{x^3})$ = 125 - 6 = 119