2016 · Q77
A circular path is made from two concentric circular rings in such a way that the smaller ring when allowed to roll over the circumference of the bigger ring, it takes three full revolutions. If the area of the pathway is equal to n times the area of the smaller ring, then n is equal to
Elementary MathematicsMensuration
- A4
- B6
- C8
- D10
Explanation
Three revolutions give 2πR = 3·2πr, so R = 3r. The pathway area is π(R²−r²) = 8πr². This is 8 times the smaller ring's area, so n = 8, option C.