If the radius of a circle is doubled, how do its circumference and area change?
ACircumference doubles and area doubles
BCircumference doubles and area becomes four times
CCircumference becomes four times and area doubles
DBoth circumference and area become four times
Answer & Solution
Correct answer: B. Circumference doubles and area becomes four times
Circumference is proportional to $r$, since $C=2\pi r$, so doubling $r$ doubles the circumference. Area is proportional to $r^2$, since $A=\pi r^2$, so doubling the radius makes the area $2^2=4$ times the original. Options A and D ignore that area depends on the square of the radius.
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