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	Options
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 question that it took 4(1/2)hrs to travel back to same point.   So,   30/15+x−30/15−x=4 1/2   30/15+  30/15= 
<gadget id="calculator">30/15+  30/15</gadget>
<output>4</output>
4 1/2=&gt;900/225−x2=9/2   =&gt;9x2=225   =&gt;x=5km/hr   Option 5 km/hr
<result>D</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