The perimeter of a circle is 44 cm. What is its radius?
Answer: 2πr = 44 ⇒ r = 44 × 744 = 7 cm.
Step-by-step solution
Given: Perimeter (circumference) = 44 cm; π = 227
To find: Radius r
To find: Radius r
Idea: Put the given perimeter into C = 2πr and solve for r.
- Circumference C = 2πr, so 2 × 227 × r = 44, i.e. 447r = 44.1 mark
- r = 44 × 744 = 7 cm.1 mark
The radius is 7 cm.
Check: 2 × 227 × 7 = 44 ✓.
Answer to write in the exam
2πr = 44
2 × 227 × r = 44
r = 44 × 744
∴ r = 7 cm
Common mistakes that cost marks
- Using πr2 = 44 (area) and getting r ≈ 3.74 cm.
- Giving the diameter (14 cm) as the radius.
How this can come in the exam
MCQ (1 mark)
The circumference of a circle is 88 cm. Its radius is (use π = 227)
- 7 cm
- 28 cm
- 44 cm
- 14 cm
Show answer
(D) 14 cm
r = 88 ÷ (2 × 227) = 88 × 744 = 14 cm.
Try one yourself
The perimeter of a circular park is 132 m. Find its radius. (Use π = 227.)
Show answer
r = 132 × 744 = 21 m.
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