Logarithmic Exponential Equation

CAT 2019 Slot 1 · Quantitative Ability · Easy · Logarithm

If xx is a positive quantity such that 2x=3log⁡522^x = 3^{\log_5 2}, then xx is equal to

  1. A.

    log⁡59\log_5 9

  2. B.

    1+log⁡5(35)1 + \log_5(\frac{3}{5})

  3. C.

    1+log⁡3(53)1 + \log_3(\frac{5}{3})

  4. D.

    log⁡58\log_5 8

Answer

B

Explanation

Taking log⁡2\log_2 on both sides: x=log⁡2(3log⁡52)=(log⁡52)⋅log⁡23=log⁡2log⁡5⋅log⁡3log⁡2=log⁡3log⁡5=log⁡53x = \log_2 (3^{\log_5 2}) = (\log_5 2) \cdot \log_2 3 = \frac{\log 2}{\log 5} \cdot \frac{\log 3}{\log 2} = \frac{\log 3}{\log 5} = \log_5 3. Notice that 1+log⁡5(3/5)=log⁡55+log⁡53−log⁡55=log⁡531 + \log_5(3/5) = \log_5 5 + \log_5 3 - \log_5 5 = \log_5 3. So Option B is correct.

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