$9^3 \times (81)^2 \div (27)^3 = (3)^x$
Aptitude
Surds and Indices
Difficulty: Easy
Choose an option
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A3
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B4
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C5
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D6
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ENone of these
Answer
Correct Answer: 5
Explanation
### Concept & Formula
This problem evaluates your ability to standardize bases and apply the core laws of indices to simplify algebraic expressions.
$$ a^m \times a^n = a^{m+n} $$
$$ a^m \div a^n = a^{m-n} $$
$$ (a^m)^n = a^{mn} $$
### Step-by-Step Solution
* **Given:**
The expression to evaluate is $9^3 \times (81)^2 \div (27)^3 = (3)^x$.
* **Calculation:**
1. Observe that all numbers ($9$, $81$, $27$) are powers of the base $3$. Convert each term accordingly:
$9 = 3^2$
$81 = 3^4$
$27 = 3^3$
2. Substitute these prime bases back into the original equation:
$(3^2)^3 \times (3^4)^2 \div (3^3)^3 = 3^x$
3. Apply the power of a power rule to simplify the exponents:
$3^6 \times 3^8 \div 3^9 = 3^x$
4. Apply the product and quotient rules for exponents from left to right:
$3^{(6 + 8 - 9)} = 3^x$
$3^{14 - 9} = 3^x$
$3^5 = 3^x$
5. Since the bases on both sides are identical, equate the exponents:
$x = 5$
### Exam Strategy & Shortcut
Do not write out full base conversions. Mentally translate the problem purely into the powers of base $3$. You know $9$ is $3^2$, so $9^3$ gives a power of $6$. $81$ is $3^4$, so squared it gives $8$. $27$ is $3^3$, so cubed it gives $9$. Combine them directly: $6 + 8 - 9 = 5$. The answer is $5$ in seconds.
### Common Pitfall
Students often confuse the rules when raising a power to another power, mistakenly adding the exponents instead of multiplying them (e.g., computing $(3^2)^3$ as $3^5$ instead of $3^6$). Always multiply when brackets separate the powers.
### Final Answer
**Therefore, the correct answer is 5.**