Question

The radius of a circle is multiplied by 7. Its area is _____ times bigger than the original circle.

7

21

49

70

Answer 1

7^2 = 49

Answer 2

\[A = \pi r ^{2}\]
So \[A _{1} = \pi r ^{2}\]
\[A _{2} = \pi (7r)^{2}\]
\[A _{2} / A _{1} = (\pi (7r)^{2}) / (\pi r ^{2}) = 49 (\pi r ^{2} / \pi r^{2}) = 49\]