Maths / Comparing Quantities / Percentage Change

QUESTION

If radius of a circle is increassed by 10% then area of the circle will be increased by

 OPTIONS A. 50% B. 15% C. 21% D. 20%
Right Option : C

EXPLANATION
Explain TypeExplanation Content
Text

increase = 10% of r=0.1r

$\dpi{120} \fn_jvn \large Original\: Area = \pi X r^2$

$\dpi{120} \large \dpi{120} \fn_jvn \large New\: Area = \pi X (1.1r)^2 = 1.21\pi Xr^2$

$\dpi{120} \fn_jvn \large Increase= 1.21\pi Xr^2 -\pi X r^2 = 0.21 \pi r^2$

$\dpi{120} \large Percentage \: Increase= \frac{increase}{original}X 100=\frac{0.21\pi r^2}{\pi r^2} X 100$

=21 %

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