Which circle is bigger: One with an area of 30 square units or one with a circumference of 30 units? How do you know?

Circumference = 2 x pi x radius
When circumference = 30, radius = 15/pu units.

Area of circle = pi x r^2 = pi x 225/pi^2.

Since we know pi is around 3.14, we can use that as an approximation and get the area of the circle with 30 units circumference to be around 72 squared units.

Hence, the circle with circumference of 30 units is much bigger.