At the same speed a boat travelling 50km upstream and 78km downstream in 16hrs. Also it can travel 70km upstream and 104km downstream, in 22hrs at the same speed of the stream is.

Let U be the upstream speed and D be the downstream speed, which gives the equations 50/U + 78/D = 16 and 70/U + 104/D = 22. Multiplying the first equation by 4 and the second equation by 3, then subtracting the second from the first, eliminates D and yields -10/U = -2, so U equals 5 km/h. Substituting U into the first equation gives 10 + 78/D = 16, which means 78/D equals 6 and D equals 13 km/h. Using the formula for the speed of the stream, we calculate one half of the difference between the downstream and upstream speeds, which is one half of (13 minus 5), resulting in a stream speed of 4 km/hr.

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