The speed of a boat in still water (b) is 50km/h. It takes the same time (t) for the boat to travel 10km (x) upstream as it does to travel 20km (y) downstream. Find the speed of the current.
upstream speed (u) = speed in still water (b) - stream speed (s) = b-s = 50-s
downstream speed (d) = speed in still water (b) + stream speed (s) = 50+s
time (t) = x/u = y/d
10/(50-s) = 20/(50+s)
10(50+s) = 20(50-s)
500 + 10s = 1000 - 20s
30s = 500
stream speed (s) = 500/30 = 16.6 km/h
