Теплоход прошёл 28 км против течения реки и вернулся обратно, потратив на обратный путь на 4 мин меньше. Найти скорость теплохода в стоячей воде, если скорость течения реки составляет 1 км/ч.

Let's assume the speed of the boat in still water is "x" km/h.

When the boat is going against the current, its effective speed is reduced by the speed of the current. So, the speed of the boat against the current is (x - 1) km/h.

On the way back, when the boat is moving with the current, its effective speed is increased by the speed of the current. So, the speed of the boat with the current is (x + 1) km/h.

We know that the boat takes 4 minutes less time on the return journey compared to the journey against the current.

Since speed = distance / time, we can create the following equation:

28 / (x - 1) = 28 / (x + 1) - 4/60

To solve this equation, we need to eliminate the fractions. We can do that by multiplying the entire equation by the least common multiple (LCM) of the denominators, which is 60:

28 * 60 = 28 * (x + 1) - 4

1680 = 28x + 28 - 4

1680 - 28 + 4 = 28x

1656 = 28x

x = 1656 / 28

x ≈ 59.14

Therefore, the speed of the boat in still water is approximately 59.14 km/h.