The boat sails some distance along the lake in 5 hours, and along

The boat sails some distance along the lake in 5 hours, and along the river in 3 hours. How long does it take for a raft to travel the same distance?

1. Own speed of the boat: Vc km / h;

2. River flow speed: Vp km / h;

3. In the lake the boat sailed time: T1 = 5 hours;

4. Time for sailing the boat along the river: T = 3 hours;

5. Distance traveled along the river and lake: S km;

6. We compose the equation of motion of the boat:

S = T1 = Vc = 5 * Vc km;

S = T2 * (Vc + Vp);

5 * Vc = 3 * (Vc + Vp);

2 * Vc = 3 * Vp;

Vc = 1.5 * Vp;

Time of sailing a raft at a distance S: To = S / Vp = (5 * Vc) / Vp =

(5 * (1.5 * Vp) / Vp = 7.5 hours;

Answer: the time of movement of the raft is 7.5 hours.