The speed of a boat in still water is 10 km/hr. The stream has a current of 2km/hr. The boat takes 2 hours more to cover a trip from A to B than it took to go from B to A. What is the distance between A and B?
30 km
16 km
48 km
40 km
32 km

• Speed of boat=10,speed of stream=2,time=2 hr
  Let distance be x
  (x/(10-2))-(x/(10+2))=2
  x/8-x/12=2
  x=48
• 6 years agoHelpfull: Yes(5) No(0)
• ans is 48
  given that
  x=10,y=2
  for downstream x+y=d/t 10+2=d/t------1
  for upstream x-y=d/t+2 10-2=d/t+2-------2
  solving 1 &2 we get
  time=4
  and distance= 48
• 6 years agoHelpfull: Yes(1) No(0)
• (10+2)*x=(10-2)*(x+2)
  x=4
  hence AB=4*12
  =48
• 6 years agoHelpfull: Yes(1) No(0)
• Shortcut method to find a solution
  Let Distance be D, boat speed be x , stream speed be y ,Time be t
  (2 × D × y)÷[(x+y)×(x-y)] = t
  2D ×2/(12×8) =2
  Solving D=48
• 5 years agoHelpfull: Yes(1) No(0)
• Let u be the speed of the boat in still water : u = 10 km/hr
  Let v be the speed of the current : v = 2 km/hr
  
  Let time from B to A = t hrs
  Therefore, time from A to B = (t + 2) hrs
  
  Since the time from A to B is more than the time from B to A, we get the idea that A to B is upstream (and B to A is downstream).
  
  Speed of the boat upstream = 10 + 2 = 12 km/hr
  Speed of the boat downstream = 10 - 2 = 8 km/hr
  
  Distance from A to B (upstream) = Distance from B to A (downstream)
  Therefore, with the help of Distance = Speed x Time;
  
  8 x (t + 2) = 12 x t
  8t + 16 = 12t
  16 = 12t - 8t
  16 = 4t
  Therefore, t = 4hrs ............ (i)
  
  Now,putting (i) into either of the distance expressions (either upstream or downstream), we will get the answer.
  
  (I have taken the downstream expression)-
  
  Distance (A to B or B to A) = 12 x t = 12 x 4 = 48 kms ............ (Answer)
• 5 years agoHelpfull: Yes(0) No(0)