A small ring of negligible thickness and radius 2 cm moves on a bigger rung of radius 10 cm. How many rotations will the small ring take on the bigger ring to make a complete round ?
Options:
A . 5
B . 6
C . 7
D . 10
Answer: Option A Required number of rotations : $$\eqalign{ & = \frac{{{\text{Circumference of bigger ring}}}}{{{\text{Circumference of smaller ring}}}} \cr & = \frac{{2 \times \pi \times 10}}{{2 \times \pi \times 2}} \cr & = 5 \cr} $$
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