Question

Two piers, A and B, are located s km away from each other along a river. A motor boat, with a speed of vkm/hour in still water, is cruising between the two piers. How much time t (in hours) will the motorboat need to get from pier A to pier B and back, if the speed of the current is 5km/hour? Find t if: s=105, v=40

Answer 1

Speed in still water is v=40
speed of current is 5km/h
upstream speed: v-5=35
downstream speed: v+5=45
upstream time: 105/35=3
downstream time: 105/45=$2\frac{1}{3}$
total time: 3+$2\frac{1}{3}$=$5\frac{1}{3}$=5 hours 20 minutes