Question

Find the area of a circular ring formed by two concentric circles whose radii are $5.7cm$ and $4.3cm$ respectively (Take $\pi =3.1416$)

• A. $43.98$ sq. cm
• B. $53.67$ sq. cm
• C. $47.24$ sq. cm
• D. $38.54$ sq. cm

Answer 1

The correct option is A $43.98$ sq. cm

Let the radii of the outer and inner circles be $r_2$ and $r_1$ respectively; we have
$Area=\pi r_2^2-\pi r_1^2=\pi (r_2^2-r_1^2)$
$=\pi (r_2-r_1)(r_2+r_1)$
$=\pi (5.7-4.3)(5.7+4.3)=\pi \times 1.4\times 10$ sq. cm
$=3.1416\times 14sq.cm.=43.98$ sq. cm