A motorboat whose speed is 15 kmph in still water goes 30 kmph downstream and comes back in a total of 4hrs 30min the speed of the stream in kmph is

• if we read question carefully...the speed of motor boat in downstream = 30 kmph(not 30 km)
  therefore, speed of the stream= 30-15
  => 15 kmph
  
• 12 years agoHelpfull: Yes(41) No(25)
• 5 km/hr.
  
  Let the speed of the stream be x km/hr. Then,
  
  Speed downstream = (15 + x) km/hr,
  Speed upstream = (15 - x) km/hr.
  Therefore,
  30/(15+x) + 30/(15-x) = 4(1/2)
  => 900/(225-x^2) = 9/2
  => 9x^2 = 225
  => x^2 = 25
  => x = 5
  
• 12 years agoHelpfull: Yes(32) No(27)
• Speed in Down Stream(Boat+Stream)=30 Kmph
  Speed in Still Water=15 Kmph
  Speed of The Stream[(Boat+Stream)-Boat]=30-15 = 15 Kmph
• 12 years agoHelpfull: Yes(19) No(11)
• Let the speed of the stream be x km/hr. Then,
  speed downstream =(15 + x)km/hr
  
  Speed upstream = (15 - x) km/hr.
  
  Time= Distance/speed
  
  30/15+x + 30/15-x = 9/2
  
  On solving, 900/225-x^2 = 9/2
  
  x^2=25
  
  x=5km/hr
  
  
  
  x = 5 km/hr.
• 12 years agoHelpfull: Yes(15) No(10)
• 5 kM/HR
  Let the speed of the sream is x km/hr
  speed of upstream=15+x
  speed of down stream=15-x
  30/15+x+30/15-x=9/2
  solving this we get x^2=25
  x=5 km/hr
• 12 years agoHelpfull: Yes(11) No(22)
• 5km/hr....let speed of stream be x then 30/(15-x)+ 30/(15+x)=9/2
  
  x^2=25 so x=5!!!whe 30/(15-x)is time fo upstream and 30/(15+x)is downstream ..and the sum eqls total time..
• 12 years agoHelpfull: Yes(6) No(11)
• Let the speed of the stream be x km/hr. Then,
  
  Speed downstream = (15 + x) km/hr,
  
  Speed upstream = (15 - x) km/hr.
  
  30 + 30 = 4 1
  (15 + x) (15 - x) 2
  900 = 9
  225 - x2 2
  9x2 = 225
  
  x2 = 25
  
  x = 5 km/hr.
• 12 years agoHelpfull: Yes(5) No(14)
• then how did it come back?? :)
• 12 years agoHelpfull: Yes(4) No(0)
• speed of boat B is = (d+u) / 2
  speed of stream S is= (d-u) / 2 where d for downstream and u for upstream
  given that speed of boat =15km/h
  and downstream d= 30 km/h
  put the value 15= (30+u)/2
  so we get u = 0 km/h
  put the value in the stream formula s= (30-0)/2
  speed of stream is = 15km /h ---> [answer].
  
  we can prove it given time is 4hrs and 30 min= 9/2
  t = d/s
  d/15 + d/30 = 9/2 so distance =45 km
  time required for for 45 km is
  45/15 = 3 hrs
  45/30 = 1.5 hrs
  so 3 + 1.5 = 4.5 ( 4 hrs 30 min) -----/ proved
• 8 years agoHelpfull: Yes(3) No(0)
• 5 km/hr.
  
  Let the speed of the stream be x km/hr. Then,
  
  Speed downstream = (15 + x) km/hr,
  Speed upstream = (15 - x) km/hr.
  Therefore,
  30/(15+x) + 30/(15-x) = 4(1/2)
  => 900/(225-x^2) = 9/2
  => 9x^2 = 225
  => x^2 = 25
  => x = 5
• 11 years agoHelpfull: Yes(2) No(1)
• Let the speed of the stream be x km/hr. Then,
  
  Speed downstream = (15 + x) km/hr,
  
  Speed upstream = (15 - x) km/hr.
  
  30 + 30 = 4 1
  (15 + x) (15 - x) 2
  900 = 9
  225 - x2 2
  9x2 = 225
  
  x2 = 25
  
  x = 5 km/hr.
  
• 9 years agoHelpfull: Yes(2) No(0)
• The question might be wrong if it is 30km distance then the answer 5km/hr could be the answer
• 11 years agoHelpfull: Yes(1) No(0)
• if speed of stream is 15 kmph(i.e 30 -15 =15 kmph)then it relative velocity of boat with respect to stream will be zero("0"),so it will not come back .
  
• 11 years agoHelpfull: Yes(0) No(1)
• let speed of boat=a
  speed of stream=b
  now we have a=DOWNSTREAM+UPSTREAM/2
  b=DOWNSTREAM-UPSTREAM/2
  in question we have asked stream speed
  threrefore b=DS-US/2=30-15/2=15/2=7.5
  ans=7.5
• 8 years agoHelpfull: Yes(0) No(0)
• speed of the boat = 15 kmph
  speed of the boat stiill in water means ( speed of the boat + speed of the stream ) = 30 kmph
  therefore, speed of the stream = (speed of boat+ speed of stream ) - speed of boat
  i.e..,, 30-15 = 15kmph.
  
• 8 years agoHelpfull: Yes(0) No(1)
• Explanation:
  Let the speed of the stream be x km/hr. Then,
  Speed downstream = (15 + x) km/hr,
  Speed upstream = (15 - x) km/hr
  
  So we know from question that it took 4(1/2)hrs to travel back to same point.
  
  So,
  3015+x−3015−x=412=>900225−x2=92=>9x2=225=>x=5km/hr
  3015+x−3015−x=412=>900225−x2=92=>9x2=225=>x=5km/hr
  
• 8 years agoHelpfull: Yes(0) No(0)