The boat sails 25 km against the current and 36 km along the course of the river in the same time.

The boat sails 25 km against the current and 36 km along the course of the river in the same time. find the speed of the river if the boat’s own speed is 17 km / h.

First, let’s create a table:

U total, km / h U proper, km / h U current, km / h S, km t, h Upstream 17 – х 17 х 25 25/17 – х Downstream 17 + х 17 х 36 36/17 + х
We know that the travel time is the same downstream and upstream, so we can equate them:

25/17 – x = 36/17 + x;

25/17 – x – 36/17 + x = 0;

25 (17 + x) – 36 (17 – x) / (17 – x) (17 + x) = 0;

425 + 25x – 612 + 36x / (17 – x) (17 + x) = 0;

61x – 187 / (17 – x) (17 + x) = 0;

(17 – x) (17 + x) cannot = 0;

x cannot = 17; – 17.

61x – 187 = 0;

x = 187/61 = 3 4/61 km / h.