Answers

2014-09-04T16:39:17+05:30
Let the distance be x km/hr
CASE 1 
while going to a place (upstream)
distance = x km
speed =( 5-3) km/hr
           =2 km/hr
time =  \frac{x}{2} hr -------------------> (1)

CASE 2
while coming back (downstream)
distance = x km
speed = (3+2) km/hr
           =5 km/hr
time =  \frac{x}{5} km/hr-------------- > (2)

From (1) and (2)
 \frac{x}{2} + \frac{x}{5} =3
 \\  \frac{5x+2x}{10}=3
 \\ 7x=30
 \\ x= \frac{30}{7} 
 \\ x=4.28
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2014-09-04T20:16:03+05:30
Speed of the boat in still water =5km/h
speed of steam=3km/h
time takes to row to one place to other=3hours
 time taken in up stream=  \frac{x}{5-3}= \frac{x}{2}
time taken in downstream = \frac{x}{5+3} =  \frac{x}{8}
total time = \frac{x}{2} +  \frac{x}{8} =3
   \frac{4x}{2} + \frac{x}{8} =3
   \frac{5x}{8} = 3   5x=24
  x=24/5   x=4.8
  hence required distance=4.8


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