A boat takes 38 hours for travelling downstream from place P to place Q and coming back to a place R midway between P and Q. if the velocity of the stream is 8 km/hr and the speed of the boat in still water is 28 km/hr, what is the distance between P and R ?
Speed downstream = (28 +8) = 36 km/hr;
Speed upstream = (28 -8) = 10 km/hr
Let the distance between P and Q be x km.
then, x/36 + (x/2)/20 = 38
=> x/36 + x/40 = 38
=> (10x+9x)/360 = 38
=> 19x = 38*360
x = 720 km. hence, distance between P and R is x/2 = 360 km
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