Subject: General Aptitude · Chapter: Area · Exam: 2010 · Marks: · Difficulty:
The ratio of the radii of two circles is 1 : 3. Then the ratio of their areas is
(a)1 : 3
(b)1 : 6
(c)1 : 9
(d)None of these
Answer
Answer (as printed): C
Explanation
Let the radii of the two circles be $r$ and $3 r$ respectively. $$\text { Then, required ratio }=\frac{\pi r^{2}}{\pi(3 r)^{2}}=\frac{\pi r^{2}}{9 \pi r^{2}}=1: 9 .$$
Explanation as extracted from the printed page; notation may be imperfect.