The area of a circle is 220 sq. cm. The area of a square inscribed in this circle will be
Aptitude
Area
Difficulty: Medium
Choose an option
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A49 cm²
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B70 cm²
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C140 cm²
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D150 cm²
Answer
Correct Answer: 140 cm²
Explanation
### Concept & Inscribed Square
For a square inscribed inside a circle, the diagonal of the square is equal to the diameter of the circle ($2r$). The area of a square can be found directly from its diagonal $d$.
$$Area\ of\ Square = \frac{d^2}{2} = \frac{(2r)^2}{2} = 2r^2$$
### Step-by-Step Solution
* Given Area of the circle $= 220$ cm².
* Formula for circle area: $\pi r^2 = 220$.
* Solve for $r^2$:
$\frac{22}{7} \times r^2 = 220$
$r^2 = \frac{220 \times 7}{22} = 10 \times 7 = 70$.
* The diagonal ($d$) of the inscribed square equals the diameter of the circle ($2r$).
* Area of the square $= \frac{1}{2} \times d^2 = \frac{1}{2} \times (2r)^2 = \frac{1}{2} \times 4r^2 = 2r^2$.
* Substitute the value of $r^2$ into the area formula:
$Area = 2 \times 70 = 140$ cm².
### Exam Strategy & Shortcut
Memorize the direct relationship: Area of Inscribed Square $= \frac{2}{\pi} \times Area\ of\ Circle$.
Using $\pi = \frac{22}{7}$, Area of Square $= Area\ of\ Circle \times \frac{7}{11}$.
Therefore, $220 \times \frac{7}{11} = 20 \times 7 = 140$ cm². This skips solving for $r$ entirely.
### Common Pitfall
A common mistake is finding $r^2=70$ and then trying to take the square root to find $r$, which leads to messy decimals. Always look at what the final formula requires; here it needs $r^2$, so leave it as $70$.
### Final Answer
Therefore, the correct answer is **140 cm²**.