The ratio of areas of two circles is 81 : 121. What will be the ratio of their circumferences ?

9 : 11

Area of circle = \(\Pi \)\( {r }^{2 } \)

Circumference of a circle = 2\(\Pi \)r

⇒ Ratio of circles A and B = 81 : 121

⇒ \(\Pi \)\( {r }^{2 } \)A = 81,   \(\Pi \)\( {r }^{2 } \)B = 121

⇒ \(\Pi \)r A= 9,    \(\Pi \)r B = 11.

⇒ Circumference ratio = 2\(\Pi \)9 : 2\(\Pi \)11

⇒ 9 : 11.