ABC26GN4549 · Area

Subject: General Aptitude · Chapter: Area · Exam: · Marks: · Difficulty:

The sum of areas of two circles $A$ and $B$ is equal to the area of a third circle $C$ whose diameter is 30 cm. If the diameter of circle A is 18 cm, then the radius of circle B is

(a)10 cm

(b)12 cm

(c)15 cm

(d)18 cm

Answer

Answer (as printed): B

Explanation

$\pi R_{1}{ }^{2}+\pi R_{2}{ }^{2}=\pi R_{3}{ }^{2} \Leftrightarrow R_{1}{ }^{2}+R_{2}{ }^{2}=R_{3}{ }^{2} \Leftrightarrow(9)^{2}+R_{2}{ }^{2}=(15)^{2}$ $$\begin{aligned} & \Leftrightarrow R_{2}^{2}=(15)^{2}-(9)^{2}=144 \\ & \Leftrightarrow R_{2}=12 \mathrm{cm} . \end{aligned}$$

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