The boat followed the river from pier A to pier B and returned. The speed of the river flow is 3 km / h

The boat followed the river from pier A to pier B and returned. The speed of the river flow is 3 km / h. Find the speed of the boat in still water if: a) the boat went from A to B for 1.5 hours, and from B to A – 2 hours; b) the speed of the boat against the stream of the river is 75% of the speed with the stream.

1. We take for x the speed of a river vessel in still water.

a) If the travel time of a river vessel from pier A to pier B and back is known, we compose the equation:

1.5 (x + 3) = 2 (x – 3);

1.5x + 4.5 = 2x – 6;

0.5x = 10.5;

x = 21 km / h.

b) If it is known that the speed of the vessel against the flow of water in the river is equal to 75% of the speed in the direction of the flow of water in the river, we compose the equation:

(x – 3) = 0.75 (x + 3);

x – 3 = 0.75x + 2.25;

0.25x = 5.25;

x = 21 km / h

Answer: the speed of a river vessel in still water is 21 km / h.

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