A semicircular window has diameter 63 cm.\nFind its perimeter (the curved edge plus the straight diameter).

Difficulty: Easy

Correct Answer: 162

Explanation:


Introduction / Context:
Perimeter of a semicircle consists of the semicircular arc plus the straight diameter edge. Recognizing this avoids the common mistake of using only the curved length.


Given Data / Assumptions:

  • Diameter D = 63 cm.
  • Radius r = D/2 = 31.5 cm.
  • Perimeter P = arc length (half circumference) + diameter.


Concept / Approach:
Full circumference is 2 * pi * r. Half of that is pi * r. Therefore P = pi * r + D. Using pi = 22/7 works neatly with multiples of 7.


Step-by-Step Solution:

r = 31.5 cm = 63/2 cmArc length = pi * r = (22/7) * (63/2) = (22 * 9) / 2 = 99 cmPerimeter P = arc + diameter = 99 + 63 = 162 cm


Verification / Alternative check:
Compute half circumference as (pi * D)/2 + D = (22/7 * 63)/2 + 63 = (198)/2 + 63 = 99 + 63 = 162 cm. Same result confirms consistency.


Why Other Options Are Wrong:

  • 132, 142, 172: Each misses the exact arithmetic from using pi = 22/7 with D divisible by 7. 132 would be the half circumference only if r were 42, which it is not.


Common Pitfalls:

  • Forgetting to add the diameter after computing the arc.
  • Using 2 * pi * r instead of pi * r for the arc portion.


Final Answer:
162

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