Open Middle®
Directions: Which circle is bigger? Circle A with an area of 25 square units or Circle B with the equation x^2 + y^2 = 25
Hint
How can you determine the radius of each circle?
Answer
Circle A has an area of 25 square units so its radius is about 2.8 units long. Circle B has a radius of 5 units. So, Circle B is bigger.
Source: Robert Kaplinsky
The radius of circle A is not needed. Seems simpler to me to observe that the radius of circle B is 5, and so its area is 5 x 5 x pi, which is definitely bigger than 25
Thanks Howard. You are totally right. That’s why the site is called Open Middle: there are multiple ways to solve most problems and the conversations that come out of comparing the various methods can be very valuable.