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The area of the ring between two concentric circles, whose circumference are 88 cm and 132 cm, is :
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- 780 cm²
- 770 cm²
- 715 cm²
- 660 cm²
- 780 cm²
Correct Option: B
According to question, Circumference of outer circle
= 2πr = 132 cm
| ⇒ r = | × 7 = 21 cm | |
| 2 × 22 |
Circumference of inner circle = 2πr1 = 88cm
| ⇒ r1 = | × 7 = 14 cm | |
| 2 × 22 |
∴ Area of outer circle = πr²
| = | × 21 × 21 = 1386 cm² | |
| 7 |
and Area of inner circle = πr1²
| = | × 21 × 21 = 1386 cm² | |
| 7 |
∴ Area of ring = (1386 – 616) cm² = 770cm²
