$\sqrt[3]{4\frac{12}{125}} = x$
Aptitude
Square Root and Cube Root
Difficulty: Medium
Choose an option
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A$1\frac{2}{5}$
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B$1\frac{3}{5}$
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C$1\frac{4}{5}$
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D$2\frac{2}{5}$
Answer
Correct Answer: $1\frac{3}{5}$
Explanation
Concept & Strategy
To find the root of a mixed fraction, you must first convert it into an improper fraction. Once converted, apply the cube root separately to the numerator and the denominator using standard radical properties.
Step-by-Step Solution
* **Given expression**:
$$\sqrt[3]{4\frac{12}{125}}$$
* Convert the mixed fraction $4\frac{12}{125}$ to an improper fraction:
$$\text{Numerator} = (4 \times 125) + 12 = 500 + 12 = 512$$
$$\text{Fraction} = \frac{512}{125}$$
* Apply the cube root to the new improper fraction:
$$\sqrt[3]{\frac{512}{125}} = \frac{\sqrt[3]{512}}{\sqrt[3]{125}}$$
* Evaluate the cube roots of these known perfect cubes:
$$\sqrt[3]{512} = 8$$
$$\sqrt[3]{125} = 5$$
* The resulting fraction is $\frac{8}{5}$. Convert this back to a mixed fraction for the final answer:
$$\frac{8}{5} = 1\frac{3}{5}$$
Exam Strategy & Shortcut
Memorize standard cubes up to $10$. Once you see the denominator is $125$, you know its cube root is $5$. The numerator becomes $512$ ($4 \times 125 + 12$). Since $\sqrt[3]{512}$ is $8$, the fraction $8/5$ quickly converts to $1\frac{3}{5}$ in your head.
Common Pitfall
Attempting to take the cube root of the whole number ($4$) and the fraction piece ($\frac{12}{125}$) separately. This mathematically violates radical rules and leads to nonsensical dead ends. Always convert to improper fractions first.
Final Answer
**Therefore, the correct answer is $1\frac{3}{5}$.**