Question

Ram can row a boat 8km downstream and return in 1hour 40mins. If speed of the stream is 2Km/hr, find the speed of boat in still water.

Please help!

Answer 1

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