A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:	Select.
A) 5kmph  B) 7kmph  C) 6kmph  D) 4kmph  E) 4.5kmph
Let the speed of the stream be x km/hr. Then,   Speed downstream = (15 + x) km/hr,   Speed upstream = (15 - x) km/hr.   30/(15+x) + 30/(15-x) = 4.5   9 * x^2 = 225   x^2 = 25   x = 5 kmph   5kmphns- 5kmph
<result>A</result>
A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is: