Two circles are concentric with circumference 154 cm and 88 cm respectively. Find the area of ring?
Answer & explanation
Correct answer: option 1
OP = r2 , OQ = r1
Area of ring = πr22 - πr12
circumference of circle (OP) = 2πr2 = 154
⇒ r2 = \(\frac{154 × 7}{22 × 2}\) = \(\frac{49}{2}\) = 24.5
Circumference of circle OQ = 2πr1 = 88
⇒ r1 = \(\frac{88 × 7 }{22 × 2}\) = 14
Area of ring = πr22 - πr12
= π(r1+r2) (r2 -r1)
= π (10.5) (38.5) = 1270.5 cm2