3. In a lake, a stream flows in, adding the same amount of water to the lake every day. 183 horses can drink all the water today, i.e., they would empty the lake in 24 hours, and 37 horses, starting from today, can drink all the water in 5 days. How many days, starting from today, would it take for one horse to drink all the water?
Solution. Let $x$ be the amount of water initially in the lake, $y$ be the amount of water the stream adds to the lake in one day, and $z$ be the amount of water one horse drinks in one day. Then

$$
183 z = x + y, \quad 5 \cdot 37 z = x + 5 y
$$

From these equations, we get

$$
185 z - 183 z = (x + 5 y) - (x + y), \text{ i.e., } 2 z = 4 y
$$

Furthermore,

$$
z = 2 y \text{ and } x = 183 z - y = 365 y
$$

Let $n$ be the number of days it takes for one horse to drink all the water. Then $x + n y = n z$, from which we get

$$
n = \frac{x}{z - y} = \frac{365 y}{2 y - y} = 365 \text{ days. }
$$