The value of $\log_{343} 7$ is
Aptitude
Logarithm
Difficulty: Medium
Choose an option
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A$\frac{1}{3}$
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B$-3$
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C$-\frac{1}{3}$
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D$3$
Answer
Correct Answer: $\frac{1}{3}$
Explanation
Concept & Formula
When the base of a logarithm is larger than the argument, expect a fractional exponent. Use the base change or exponent conversion rule:
$$ \log_a b = x \implies a^x = b $$
Step-by-Step Solution
* **Given:** Evaluate $\log_{343} 7$.
* **Calculation:** Let the unknown value be $x$.
$$ \log_{343} 7 = x $$
* Convert the logarithmic equation into an exponential equation:
$$ 343^x = 7 $$
* Recognize that $343$ is a perfect cube of $7$, meaning $343 = 7^3$. Substitute this into the equation:
$$ (7^3)^x = 7^1 $$
$$ 7^{3x} = 7^1 $$
* Since the bases are identical, equate the exponents:
$$ 3x = 1 $$
$$ x = \frac{1}{3} $$
Exam Strategy & Shortcut
If you memorize cubes up to $10$, you will instantly spot that $7^3 = 343$. Since the logarithm asks "what power of $343$ gives $7$", taking the cube root (power of $1/3$) is the immediate mental answer.
Common Pitfall
Students often answer with $3$ instead of $1/3$, confusing $\log_{343} 7$ with $\log_7 343$. Always pay attention to which number is the base and which is the argument.
Final Answer
**Therefore, the correct answer is \frac{1}{3}.**