The motor boat covered 48 km along the river in 4 hours. The river speed is 2.5 km / h. What is the motor boat’s own speed?

1) Let’s designate the boat’s own speed as x km / h.
2) The speed of the boat along the current will be determined as the sum of its own speed and the speed of the river: (x + 2.5) km / h.
3) Multiplying the speed of the boat by time, we find the value of the distance traveled:
(x + 2.5) * 4 (km).
4) It is known that in 4 hours the boat traveled 48 km downstream, so we make up the equality:
(x + 2.5) * 4 = 48.
5) Solve the equation:
4x + 4 * 2.5 = 48;
4x + 10 = 48;
4x = 48 – 10;
4x = 38;
x = 38: 4;
x = 9.5.
6) x = 9.5 km / h – the boat’s own speed.
Answer: 9.5 km / h.