9. While thinking about a math problem, Francesco walks back and forth as usual, taking 1 step forward, 2 steps backward, 3 steps forward, 4 steps backward, and so on (with each step being $60 \mathrm{~cm}$). As soon as he reaches 30 meters from the starting point, he finally solves the problem. How many steps will he have taken in total?
(A) 50
(B) 5150
(C) 1275
(D) 5050
(E) 4950
Problem 9. The correct answer is (E).

It is convenient to measure in steps: 30 meters correspond to 50 steps of distance. The first time Francesco reaches a new distance (integer) from the starting point (greater than those reached previously), this always happens at the end of a forward walking segment. More precisely, the distance of $n$ steps from the starting point is reached for the first time at the end of the walking segment of $2 n-1$ steps forward. The number of steps up to that point will be

$$
1+2+3+\ldots+(2 n-1)=\frac{(2 n-1) \cdot 2 n}{2}=n(2 n-1) \text {. }
$$

For $n=50$, the steps are thus $50 \cdot 99=4950$.