If the circumference of a circle increases from 4π to 8π, then its area is
(a) halved
(b) doubled
(c) tripled
(d) quadrupled
Let the circumference $C=4 \pi$
$\therefore 2 \pi r=4 \pi$
$\therefore r=2$
Therefore, area of the circle when radius of the circle is 2 can be calculated as below,
$\pi r^{2}=\frac{22}{7} \times 4$ ......(1)
Now when circumference is, then the radius of the circle is calculated as below,
$\therefore 2 \pi r=8 \pi$
$\therefore r=4$
Therefore, area of the circle when radius of the circle is 2 can be calculated as below,
$\pi r^{2}=\frac{22}{7} \times 16$
$\therefore \pi r^{2}=4\left(\frac{22}{7} \times 4\right)$.....(2)
Therefore, from equation (1) and (2) we can say that its area is quadrupled.
Hence, the correct answer is option $(d)$.