Question

7. A sailor, can raw a boat 10 km downstream and retum
back to the starting point in 50 minutes. If the speed of
the stream is 5 km/hr, find the speed of the boat is still
water​

Answer 1

Answer:Speed of stream=2 Km/h.Let speed of boat in still water be x Km/h. Time taken to travel downstream=8/(x+2). Time taken to travel upstream=8/(x-2). Total time=1 h 40 min=5/3 h. 8/(x+2)+8/(x-2)=5/3. 24(x-2)+24(x+2)=5(x+2) (x-2). 48x=5x^2-20. 5x^2-48x-20=0. x=48+√(-48)^2-4*5*(-20). x=48+√2304+400. x=48+52/10. x=100/10=10.Therefore speed of boat in still water=10km/h.