Question

If sum of inner and outer radius of circular ring is 7 cm and their difference is 1 cm, find the area of the ring.

• A. 7 $c{m}^2$
• B. 11 $c{m}^2$
• C. 14 $c{m}^2$
• D. 22 $c{m}^2$

Answer 1

The correct option is D 22 $c{m}^2$

Given : R+r = 7 cm
R-r = 1 cm
Area of a ring = $\left(\pi \right)(R^2-r^2$)
We know $(R^2-r^2)=(R+r)(R-r)$
Area of a ring = $\pi$(R+r)$\times$(R-r)
= $\frac{22}{7}$$\times$7$\times$1 = 22$c{m}^2$
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