2) The front wheel of Chiara's bicycle has a radius of $28 \mathrm{~cm}$, while the rear wheel has a radius of $16 \mathrm{~cm}$. At the end of a bicycle ride, the front wheel has made 10000 revolutions; how many revolutions has the rear wheel made during the same ride?
(A) 12000 ,
(B) 14500 ,
(C) 17500 ,
(D) 19000 ,
(E) 21000
2. The answer is $(\mathbf{C})$.

During the bicycle trip, the front wheel of Chiara's bicycle traveled $2 \cdot \pi \cdot 28 \cdot 10000$ $\mathrm{cm}$. The same distance must have been traveled by the rear wheel; therefore, if we denote by $N$ the number of revolutions made by the rear wheel, the following equality must hold:

$$
2 \cdot \pi \cdot 28 \cdot 10000=2 \cdot \pi \cdot 16 \cdot N
$$

from which we can easily find $N=17500$.

[Problem proposed by A. Colesanti.]