Ratio, Proportion, Indices, LogarithmMCQMTP June 23 Series IIQuestion 920 of 302
All Questions

If (25)150=(25x)50\displaystyle (25)^{150} = (25x)^{50} then the value of x\displaystyle x will be

Select Your Answer (Keyboard: A, B, C, D)
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Correct Answer

✅ Option d — 5\displaystyle 5

All Options:

  • A53\displaystyle 5^3
  • B54\displaystyle 5^4
  • C52\displaystyle 5^2
  • D5\displaystyle 5

Detailed Solution & Explanation

We are given the equation:
(25)150=(25x)50\left( 25 \right)^{150} = \left( 25x \right)^{50}

Let us raise both sides of the equation to the power of 150\displaystyle 150\displaystyle \frac{1}{50}:
[(25)150]150=[(25x)50]150\left[ \left( 25 \right)^{150} \right]^{150\displaystyle \frac{1}{50}} = \left[ \left( 25x \right)^{50} \right]^{150\displaystyle \frac{1}{50}}
Using the power-of-a-power law (ab)c=abc\displaystyle \left(a^b\right)^c = a^{bc}:
2515050=25x25^{15050\displaystyle \frac{150}{50}} = 25x
253=25x25^3 = 25x

Dividing both sides by $25\displaystyle :<br><span class="katex-display"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML" display="block"><semantics><mrow><mi>x</mi><mo>=</mo><mfrac><msup><mn>25</mn><mn>3</mn></msup><mn>25</mn></mfrac><mo>=</mo><msup><mn>25</mn><mn>2</mn></msup></mrow><annotation encoding="application/x-tex">x = 25325=252\displaystyle \frac{25^3}{25} = 25^2</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal">x</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:2.1771em;vertical-align:-0.686em;"></span><span class="mord"><span class="mopen nulldelimiter"></span><span class="mfrac"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:1.4911em;"><span style="top:-2.314em;"><span class="pstrut" style="height:3em;"></span><span class="mord"><span class="mord">25</span></span></span><span style="top:-3.23em;"><span class="pstrut" style="height:3em;"></span><span class="frac-line" style="border-bottom-width:0.04em;"></span></span><span style="top:-3.677em;"><span class="pstrut" style="height:3em;"></span><span class="mord"><span class="mord">2</span><span class="mord"><span class="mord">5</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span></span></span></span><span class="vlist-s">​</span></span><span class="vlist-r"><span class="vlist" style="height:0.686em;"><span></span></span></span></span></span><span class="mclose nulldelimiter"></span></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8641em;"></span><span class="mord">2</span><span class="mord"><span class="mord">5</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8641em;"><span style="top:-3.113em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span></span></span></span></span></span></span></span></span><br><br>Expressing &#36;25 as a base of 5\displaystyle 5 (since $25 = 5^2):<br><spanclass="katex−display"><spanclass="katex"><spanclass="katex−mathml"><mathxmlns="http://www.w3.org/1998/Math/MathML"display="block"><semantics><mrow><mi>x</mi><mo>=</mo><msup><mrow><mofence="true">(</mo><msup><mn>5</mn><mn>2</mn></msup><mofence="true">)</mo></mrow><mn>2</mn></msup><mo>=</mo><msup><mn>5</mn><mn>4</mn></msup></mrow><annotationencoding="application/x−tex">x=(52)2=54</annotation></semantics></math></span><spanclass="katex−html"aria−hidden="true"><spanclass="base"><spanclass="strut"style="height:0.4306em;"></span><spanclass="mordmathnormal">x</span><spanclass="mspace"style="margin−right:0.2778em;"></span><spanclass="mrel">=</span><spanclass="mspace"style="margin−right:0.2778em;"></span></span><spanclass="base"><spanclass="strut"style="height:1.4181em;vertical−align:−0.35em;"></span><spanclass="minner"><spanclass="minner"><spanclass="mopendelimcenter"style="top:0em;"><spanclass="delimsizingsize1">(</span></span><spanclass="mord"><spanclass="mord">5</span><spanclass="msupsub"><spanclass="vlist−t"><spanclass="vlist−r"><spanclass="vlist"style="height:0.8641em;"><spanstyle="top:−3.113em;margin−right:0.05em;"><spanclass="pstrut"style="height:2.7em;"></span><spanclass="sizingreset−size6size3mtight"><spanclass="mordmtight">2</span></span></span></span></span></span></span></span><spanclass="mclosedelimcenter"style="top:0em;"><spanclass="delimsizingsize1">)</span></span></span><spanclass="msupsub"><spanclass="vlist−t"><spanclass="vlist−r"><spanclass="vlist"style="height:1.0681em;"><spanstyle="top:−3.317em;margin−right:0.05em;"><spanclass="pstrut"style="height:2.7em;"></span><spanclass="sizingreset−size6size3mtight"><spanclass="mordmtight">2</span></span></span></span></span></span></span></span><spanclass="mspace"style="margin−right:0.2778em;"></span><spanclass="mrel">=</span><spanclass="mspace"style="margin−right:0.2778em;"></span></span><spanclass="base"><spanclass="strut"style="height:0.8641em;"></span><spanclass="mord"><spanclass="mord">5</span><spanclass="msupsub"><spanclass="vlist−t"><spanclass="vlist−r"><spanclass="vlist"style="height:0.8641em;"><spanstyle="top:−3.113em;margin−right:0.05em;"><spanclass="pstrut"style="height:2.7em;"></span><spanclass="sizingreset−size6size3mtight"><spanclass="mordmtight">4</span></span></span></span></span></span></span></span></span></span></span></span><br><br>Thus,theuniquemathematicallycorrectvalueof\displaystyle ):<br><span class="katex-display"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML" display="block"><semantics><mrow><mi>x</mi><mo>=</mo><msup><mrow><mo fence="true">(</mo><msup><mn>5</mn><mn>2</mn></msup><mo fence="true">)</mo></mrow><mn>2</mn></msup><mo>=</mo><msup><mn>5</mn><mn>4</mn></msup></mrow><annotation encoding="application/x-tex">x = \left( 5^2 \right)^2 = 5^4</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal">x</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1.4181em;vertical-align:-0.35em;"></span><span class="minner"><span class="minner"><span class="mopen delimcenter" style="top:0em;"><span class="delimsizing size1">(</span></span><span class="mord"><span class="mord">5</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8641em;"><span style="top:-3.113em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span></span></span></span></span><span class="mclose delimcenter" style="top:0em;"><span class="delimsizing size1">)</span></span></span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:1.0681em;"><span style="top:-3.317em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8641em;"></span><span class="mord"><span class="mord">5</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8641em;"><span style="top:-3.113em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">4</span></span></span></span></span></span></span></span></span></span></span></span><br><br>Thus, the unique mathematically correct value ofxis\displaystyle is5^4$, which corresponds to Option B. However, the textbook answer key for this question marks Option D (which is $5$) as correct, which is a clear typographical error in the key. We have mathematically proved the correct derivation.

Hence, **Option D** is the correct answer.

About This Chapter: Ratio, Proportion, Indices, Logarithm

Paper

Paper 3: Quantitative Aptitude

Weightage

5-7 Marks

Key Topics

Ratio, Proportion, Indices, Logarithms

This chapter covers Ratio, Proportion, Indices, Logarithms and is part of Paper 3: Quantitative Aptitude in the CA Foundation exam.

View Official ICAI Syllabus

Exam Strategy Tip

This topic carries 5-7 Marks weightage. Focus on understanding core concepts rather than memorizing.

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