Find the value of $(-2)^5 \times (2)^{-5} \times (3)^3$
Aptitude
Surds and Indices
Difficulty: Easy
Choose an option
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A$-108$
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B$27$
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C$(2)^{25} \times (3)^3$
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D$-27$
Answer
Correct Answer: $-27$
Explanation
### Concept & Formula
This problem tests the basic laws of indices, specifically dealing with negative bases raised to odd powers, and the product rule for identical bases with different exponents.
$$(-a)^{\text{odd}} = -a^{\text{odd}}$$
$$a^m \times a^n = a^{m+n}$$
### Step-by-Step Solution
* **Given:**
Expression to evaluate: $(-2)^5 \times (2)^{-5} \times (3)^3$
* **Calculation / Deduction:**
1. First, handle the negative sign in the first term. Since a negative number is raised to an odd power (5), the result will be negative.
$$(-2)^5 = - (2^5)$$
2. Substitute this back into the original expression:
$$- (2^5) \times (2)^{-5} \times (3)^3$$
3. Group the terms with the same base (base 2). Apply the product rule of exponents ($a^m \times a^n = a^{m+n}$):
$$- (2^{5 + (-5)}) \times (3)^3$$
$$- (2^0) \times (3)^3$$
4. Apply the zero exponent rule, which states that any non-zero number raised to the power of 0 is 1 ($a^0 = 1$):
$$- (1) \times (3)^3$$
5. Finally, calculate the cube of 3 ($3 \times 3 \times 3 = 27$) and multiply by -1:
$$-1 \times 27 = -27$$
### Exam Strategy & Shortcut
**Mental Math Simplification:** You can solve this mentally in 5 seconds. Recognize that $(-2)^5$ is simply $-32$ and $2^{-5}$ is $\frac{1}{32}$. Multiplying a number by its exact reciprocal yields 1, and preserving the negative sign gives $-1$. So the entire base-2 portion simply cancels out to $-1$. You are left with $-1 \times 3^3 = -27$.
### Common Pitfall
A common error is mishandling the negative base. Students sometimes incorrectly assume that $(-2)^5 \times (2)^{-5}$ simplifies to $(-2 \times 2)^{5-5}$ or similar flawed logic, losing track of the crucial negative sign that persists purely because the exponent is an odd number.
### Final Answer
**Therefore, the correct answer is $-27$.**