Question

The difference between circumference and diameter of a ring is 10 cm. Find the radius of the ring.

(a) 3.07 cm

(b) 0.37 cm

(c) 2.33 cm

(d) 4.57 cm

I got this question in an interview.

The above asked question is from Perimeter and Area of a Circle in division Area Related to Circles of Mathematics – Class 10

Answer 1

The correct answer is (c) 2.33 cm

To elaborate: Circumference – Diameter = 10 cm    (∵ Diameter = 2 × radius)

2πr – 2r = 10 cm

2r(π – 1) = 10 cm

2r(\(\frac {22}{7}\) – 1) = 10 cm

2r(\(\frac {15}{7}\)) = 10 cm

r = 10 × \(\frac {7}{15} \times \frac {1}{2}\)

r = 2.33 cm