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Question

The angle of a sector is 30°. If its radius is 42 cm then the length of the arc of the sector is:

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper PDF (31-Jan-2021) (Shift 1)
The correct answer is
22 cm

Sector Arc Length Calculation

To find the length of the arc of a sector, we use the formula:

Arc Length, $L = \frac{\theta}{360°} \times 2\pi r$

Where:

  • $\theta$ is the angle of the sector in degrees.
  • $r$ is the radius of the sector.
  • $\pi$ is the mathematical constant Pi (approximately $\frac{22}{7}$).

Applying the Formula

Given:

  • Angle, $\theta = 30°$
  • Radius, $r = 42$ cm

Substitute the values into the formula:

$L = \frac{30°}{360°} \times 2 \times \frac{22}{7} \times 42 \text{ cm}$

Step-by-Step Calculation

  1. Simplify the fraction of the angle:

    $\frac{30°}{360°} = \frac{1}{12}$

  2. Substitute the simplified fraction back into the formula:

    $L = \frac{1}{12} \times 2 \times \frac{22}{7} \times 42 \text{ cm}$

  3. Perform the multiplication:

    $L = \frac{1}{12} \times 2 \times 22 \times \frac{42}{7} \text{ cm}$

    $L = \frac{1}{12} \times 2 \times 22 \times 6 \text{ cm}$

  4. Further simplify:

    $L = \frac{1}{12} \times 264 \text{ cm}$

  5. Final result:

    $L = 22 \text{ cm}$

Therefore, the length of the arc of the sector is 22 cm.

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