9-1-1. A snail is crawling along a straight line. On the first day, it crawls 1 m forward and $1 / 2$ m backward. On the second day, it crawls $1 / 2$ m forward and $1 / 3$ m backward. On the third day, it crawls $1 / 3$ m forward and $1 / 4$ m backward, and so on. How far from the starting point will it be at the end of the 74th day?
Express the answer in meters.

Answer. $74 / 75$.

Solution Variant 1. The snail will be at a distance of

$$
\left(\frac{1}{1}-\frac{1}{2}\right)+\left(\frac{1}{2}-\frac{1}{3}\right)+\left(\frac{1}{3}-\frac{1}{4}\right)+\ldots+\left(\frac{1}{74}-\frac{1}{75}\right)=\frac{1}{1}-\frac{1}{75}=\frac{74}{75}
$$