A motorboat can travel at 8 km/hr in still water. It travelled 60 km downstream in a river and then returned, taking altogether 20 hours. Find the rate of flow of the river.
(a)3 kmph (b)3.5 kmph (c)2 kmph (d) 4 kmph

• Ans: 4kmph
  time=distance/speed
  speed of upstream=8-x
  speed of downstream=8+x
  total time taken=time taken to travel downstream+ time taken to travel upstream=20hours
  60/(8+x)+60/(80-x)=20
  x=4kmph
• 4 years agoHelpfull: Yes(2) No(0)