"A" is running with a velocity of 13 kmph in the direction of the river along the river bank. A boat which is at a distance of 12 km from "A" crossed him in 40 minutes by rowing against the flow of the river. If the river is flowing with a velocity of 1.5 kmph, then what is the velocity of the boat?
A 6.5 kmph
B 5 kmph
C 4.5 kmph
D 4 kmph

• B) 5 kmph
  
  If speed of boat=b kmph
  Speed of A along with the river=13+1.5=14.5 kmph
  Speed of boat against the river=b-1.5
  So the distance of 12 km. was covered with resultant speed of A+boat=14.5+b-1.5=13+b & time taken=40 min.=2/3 hrs
  So 12/[13+b] =2/3, b=5
• 9 years agoHelpfull: Yes(1) No(2)
• A) 6.5 kmph
  
  Distance covered by A in 2/3 hrs (40 mins) = 12 * (2/3)=26/3 kms
  Rest of the distance must be covered by the boat = 12 - (26/3)= 10/3 kms
  Speed of boat against the river = b-1.5 kmph
  time taken by boat = 40 mins = 2/3 hrs
  Distance covered by boat = Speed * Time = (b-1.5)* (2/3)
  But,
  (b-1.5)* (2/3) = 10/3
  On solving this we get b = 6.5 kmph
• 9 years agoHelpfull: Yes(0) No(0)
• I have given the explanation in youtube
• 9 years agoHelpfull: Yes(0) No(0)