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Question

The circumference of a circle is equal to the perimeter of an equilateral triangle. If the radius of the circle is 21 cm, what is the length of the side of the equilateral triangle?

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
44 cm

Calculating Circle Circumference

The radius of the circle is given as $r = 21$ cm.

The formula for the circumference ($C$) of a circle is $C = 2 \pi r$. Using the approximation $\pi \approx \frac{22}{7}$, we calculate the circumference:

$C = 2 \times \frac{22}{7} \times 21 \text{ cm}$

$C = 2 \times 22 \times 3 \text{ cm}$

$C = 132 \text{ cm}$

Finding Triangle Side Length

The problem states that the circumference of the circle equals the perimeter of an equilateral triangle.

The perimeter ($P$) of an equilateral triangle with side length $s$ is $P = 3s$.

Equating the circumference and the perimeter:

$C = P$

$132 \text{ cm} = 3s$

To find the side length $s$, divide the perimeter by 3:

$s = \frac{132 \text{ cm}}{3}$

$s = 44 \text{ cm}$

The length of the side of the equilateral triangle is 44 cm.

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