Which Circle Is Bigger? (High School)

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


How can you determine the radius of each circle?


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

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  1. 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.

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