If the area of a circle is 154 square cm, then the ratio of circumferences of this circle to that of the other circle, whose radius is 21 cm, is:
Answer & explanation
Correct answer: option 1
We know that,
Area of circle = πr2
Area of circle1 = 154 cm2
Radius of circle2 = 21 cm
= 154 = \(\frac{22}{7}\)× radius2
= radius2 = 49
= Radius = \(\sqrt {49}\) = 7cm
So the circumference of cicle1 = 2πr = 2 × \(\frac{22}{7}\)× 7 = 44 cm
Radius of circle2 = 21 cm
Circumference of circle2 = 2 × \(\frac{22}{7}\)× 21 = 132
Ratio of Circumference of circle1 : Circumference of circle2 = 44 : 132 = 1 : 3