Question

Area of ring is 28.26 $c{m}^2$ if inner radius is 4 cm, find the outer radius. (take $\pi$ = 3.14)

• A. 6 cm
• B. 5.5 cm
• C. 5 cm
• D. 4.5 cm

Answer 1

The correct option is C 5 cm

Area of ring = $\pi$$(R^2-r^2$)
28.26 = 3.14$(R^2-4^2$)
$\frac{28.26}{3.14}$ = $R^2-4^2$
9 = $R^2-16$
$R^2$ = 16+9 = 25
$⟹$ $R$ = $\sqrt{2}5$ = 5 cm