Question

The area of the ring between two concentric circles, whose circumference are 88 cm and 132 cm, is :

• A. 780
• B. 770
• C. 715
• D. 660

Answer 1

Answer:

B. 770

.

According to question,

Circumference of outer circle $= 2\pi{r} = 132 cm$

$r=\frac{132}{2\times{22}}\times{7}=21cm$

Circumference of inner circle $= 2\pi{r_1} = 88cm$

$r_1=\frac{88}{2\times{22}}\times{7}=14 cm$

Area of outer circle $= \pi{r^2}$

$=\frac{22}{7}\times{21}\times{21}$

$=1386cm^2$

and Area of inner circle $=\pi{r^2_1}$

$=\frac{22}{7}\times{14}\times{14}$

$=616cm^2$

Area of ring $=1386-616=770cm^2$