Subject: General Aptitude · Chapter: Volume and Surface Area · Exam: · Marks: · Difficulty:
Surface area of a sphere is $2464 \mathrm{cm}^{2}$. If its radius be doubled, then the surface area of the new sphere will be :
(a)$4928 \mathrm{cm}^{2}$
(b)$9856 \mathrm{cm}^{2}$
(c)$19712 \mathrm{cm}^{2}$
(d)Data insufficient
Answer
Answer (as printed): B
Explanation
Let the original radius be $r$. Then, original surface area $$=4 \pi r^{2}=2464 \mathrm{cm}^{2} \text { (given). }$$ New radius $=2 r . \therefore$ New surface area $=4 \pi(2 r)^{2}$ $$=4 \times 4 \pi r^{2}=(4 \times 2464) \mathrm{cm}^{2}=9856 \mathrm{cm}^{2} .$$