A square has side length 10. A circle with radius 3 is cut out from the center of the square. In terms of π, what is the remaining area of…

The remaining area is the square's area minus the circle's area. The square has area $10^2 = 100$. The circle has radius 3, so its area is $\pi (3)^2 = 9\pi$. The remaining area is $100 - 9\pi$, choice B. Choice A ($100 - 3\pi$) uses the radius instead of the radius squared. Choice C ($100 - 6\pi$) uses the diameter $2r$ or the formula $2\pi r$ ($6\pi$), which is the circumference, not the area. Choice D ($91\pi$) subtracts the numbers before attaching $\pi$, which mixes a plain number with a multiple of $\pi$.