**Puzzle:** A group of **25 tourists** had to cross a wide and **deep river** with no bridge in sight. They notice **two 10-year-old boys** playing in a rowboat by the shore. The problem is that the boat is so small, that it can only hold two boys or one tourist. How can the tourists get across the river and leave the boys in joint possession of the boat?

**Solution:**

Let’s solve this problem step-by-step.

- The initial situation is:
- At first, the two boys will take the boat to the other side, as shown in the figure.
- Then, one boy will return with the boat, and one boy will stay at the other end.
- When the boy returns, then one of the tourists will row the boat across the river.
- When the tourist will reach the other end, the boy there will come back with the boat.

Hence, for 1 tourist to cross the river, the boat needs to be rowed 4 times. So, for 25 tourists, the boat needs to be rowed 100 times from shore to shore. Also, **for n tourists in total 4n tourists are required.**

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