A motor boat covers a certain distance downstream in 30 minutes, while it comes back in 45 minutes. If the speed of the stream is 5 kmph what is the speed of the boat in still water?
(a) 10 kmph
(b) 15 kmph
(c) 20 kmph
(d) 25 kmph

• let speed of boat is x in still water
  then (x+5)*30=(x-5)*45
  2x+10=3x-15
  x=25 kmph
  
• 11 years agoHelpfull: Yes(47) No(3)
• Speed of boat = b km/hr
  Speed of stream = s km/hr
  Upstream speed = b-s km/hr
  Downstream speed = b+s km/hr
  Let x km be the distance
  Therefore, downstream = x*30/60 km/hr = 2x km/hr
  upstream = x*45/60 km/hr = 3x/4 km/hr
  Given speed of stream s = 5km/hr
  => s = (downstream - upstream) /2 = (2x - (4x/3))/2 => downstream = 30 km/hr
  downstream = b+s => b = downstream - s = 30 - 5 = 25 km/hr
• 11 years agoHelpfull: Yes(5) No(5)
• total speed=speed of boat+speed of stream(down stream)
  total speed=speed of boat-speed of steam(up stream)
  let speed of boat=x
  given speed of stream=5
  d/30=x+5 equation 1
  d/45=x-5 equation 2
  dividing equation 1 by 2
  we will get speed of boat =25kmph
• 11 years agoHelpfull: Yes(3) No(1)
• @Ratnesh I think it should be (5-x)*30=(5-x)*45
• 11 years agoHelpfull: Yes(0) No(10)
• let the speed of boat be sb
  upstream speed of boat is sb-5
  and distance = (sb-5)/45 ....... equ 1
  downstream speed of boat is sb+5
  and distance = (sb+5)/30 ....... equ 2
  now,equating the equ 1 and equ 2 , we get
  (sb-5)/45 = (sb+5)/30
  (sb-5)/3 = (sb+5)/2
  (sb-5)*2 = (sb+5)*3
  2 sb - 10 = 3 sb + 15
  sb = 25 kmph ... ans
  
• 11 years agoHelpfull: Yes(0) No(2)