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Problem 178

Geometry Difficulty 1.4 Multiple choice CEMC Cayley · Canada · 2026

The area of a circle with radius $K$ is $15\pi$ . The area of a circle with radius
$2K$ is

Pick one

Official solution

The area of a circle with radius $K$ is $15\pi$ , and so $\pi\times K^2=15\pi$ or $K^2=15$ .

The area of a circle with radius $2K$
is $\$\pi\times (2K)^2=\pi\times4K^2\$.$

Substituting $K^2=15$ , we get the
area of a circle with radius $2K$ is
$\pi\times4(15)=60\pi$ .

Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty, ordering) added by this project.