A motorboat, whose speed in 15 km/hr in sƟll 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	Choose one:	A) 2 km/hr	B) 3 km/hr	C) 4 km/hr	D) 5 km/hr	E) None of these
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 quesƟon that it took 4(1/2)hrs to travel back to same point.   So,   3015+x−3015−x=412=&gt;900225−x2=92=&gt;9x2=225=&gt;x=5km/hr   Answer: 5 km/hr
<result>D</result>
A motorboat, whose speed in 15 km/hr in sƟll 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