If $\log_x y = 100$ and $\log_2 x = 10$, then the value of $y$ is
Aptitude
Logarithm
Difficulty: Medium
Choose an option
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A$2^{10}$
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B$2^{100}$
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C$2^{1000}$
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D$2^{10000}$
Answer
Correct Answer: $2^{1000}$
Explanation
Concept & Formula
This problem involves solving a system of sequential logarithmic equations. You must use the fundamental definition of logarithms twice:
$$\log_a b = c \implies b = a^c$$
Additionally, you will apply the exponent rule for raising a power to a power: $(a^m)^n = a^{mn}$.
Step-by-Step Solution
* **Given:** Two equations: $\log_x y = 100$ and $\log_2 x = 10$.
* **Solving the First Variable:** Start with the equation that has a known base to find $x$.
$$\log_2 x = 10$$
* **Conversion:** Convert this to exponential form.
$$x = 2^{10}$$
* **Substituting into Second Equation:** Now look at the other given equation: $\log_x y = 100$. Convert it to exponential form to isolate $y$.
$$y = x^{100}$$
* **Combining Values:** Substitute the value of $x$ we found ($2^{10}$) into this new equation.
$$y = (2^{10})^{100}$$
* **Simplification:** Multiply the exponents together using the power rule.
$$y = 2^{10 \times 100}$$
$$y = 2^{1000}$$
Exam Strategy & Shortcut
You can solve this rapidly using the change of base property or chaining. Recognize that $y = x^{100}$ and $x = 2^{10}$. Mental substitution $(2^{10})^{100}$ immediately yields $2^{1000}$. No intermediate calculations of $2^{10}$ ($1024$) are necessary since the options remain in exponential form.
Common Pitfall
A common mistake is adding the exponents instead of multiplying them when evaluating $(2^{10})^{100}$, leading to the incorrect answer $2^{110}$. Another trap is simply multiplying $100$ and $10$ as coefficients, completely misapplying logarithm rules. Always strictly follow the power of a power rule.
Final Answer
**Therefore, the correct answer is $2^{1000}$.**