The radii of three concentric circles are in arithmetic progression. If the innermost radius is 7 cm and the outermost is 21 cm, what is the radius of the middle circle?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 14 cm.
Let the radius of the middle circle = x cm
Radii in AP: 7 cm, x cm, 21 cm
⇒ x = (7 + 21)/2 = 28/2 = 14 cm