EquationsMCQMTP June 24 Series IIIQuestion 1004 of 221
All Questions

If x+5+x16=7x+5x16\displaystyle \sqrt{x+5} + \sqrt{x-16} = \frac{7}{\sqrt{x+5} - \sqrt{x-16}} then x\displaystyle x equals

Options

A10\displaystyle 10
B20\displaystyle 20
C30\displaystyle 30
D40\displaystyle 40
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Correct Answer

Option b20\displaystyle 20

All Options:

  • A10\displaystyle 10
  • B20\displaystyle 20
  • C30\displaystyle 30
  • D40\displaystyle 40

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Detailed Solution & Explanation

Let's evaluate the equation exactly as written:
x+5+x16=7x+5x16\sqrt{x+5} + \sqrt{x-16} = \frac{7}{\sqrt{x+5} - \sqrt{x-16}}
Cross-multiplying:
(x+5+x16)(x+5x16)=7(\sqrt{x+5} + \sqrt{x-16})(\sqrt{x+5} - \sqrt{x-16}) = 7
Using the identity (a+b)(ab)=a2b2\displaystyle (a+b)(a-b) = a^2 - b^2:
(x+5)(x16)=7    21=7(x+5) - (x-16) = 7 \implies 21 = 7
This is an impossibility, meaning there is no solution. However, this is a standard typo in the test series. In the intended question, the equation is:
x+5+x16x+5x16=73\frac{\sqrt{x+5} + \sqrt{x-16}}{\sqrt{x+5} - \sqrt{x-16}} = \frac{7}{3}
Applying the Componendo and Dividendo rule:
(x+5+x16)+(x+5x16)(x+5+x16)(x+5x16)=7+373\frac{(\sqrt{x+5} + \sqrt{x-16}) + (\sqrt{x+5} - \sqrt{x-16})}{(\sqrt{x+5} + \sqrt{x-16}) - (\sqrt{x+5} - \sqrt{x-16})} = \frac{7+3}{7-3}
2x+52x16=104    x+5x16=52\frac{2\sqrt{x+5}}{2\sqrt{x-16}} = \frac{10}{4} \implies \frac{\sqrt{x+5}}{\sqrt{x-16}} = \frac{5}{2}
Squaring both sides:
x+5x16=254\frac{x+5}{x-16} = \frac{25}{4}
Cross-multiplying and solving for x\displaystyle x:
4(x+5)=25(x16)4(x+5) = 25(x-16)
4x+20=25x4004x + 20 = 25x - 400
21x=420    x=2021x = 420 \implies x = 20
Thus, x=20\displaystyle x = 20 is the unique solution to the intended system, which corresponds to Option B.
Hence, **Option B** is the correct answer.

About This Chapter: Equations

Paper

Paper 3: Quantitative Aptitude

Weightage

4-6 Marks

Key Topics

Linear, Quadratic and Cubic Equations

This chapter covers Linear, Quadratic and Cubic Equations and is part of Paper 3: Quantitative Aptitude in the CA Foundation exam.

View Official ICAI Syllabus

Exam Strategy Tip

This topic carries 4-6 Marks weightage. Focus on understanding core concepts rather than memorizing.

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