The speed of a boat in still water is 10 km/hr. If it can travel 78 km downstream and 42 km upstream in the same time, the speed of the stream is Options: A) 3 km/hr B) 12 km/hr C) 1.5 km/hr D) 4.4 km/hr E) None of these
Explanation :   Let the speed of the stream be x km/hr. Then   Speed upstream = (10-x) km/hr   Speed downstream = (10+x) km/hr   Time taken to travel 78 km downstream = Time taken to travel 42 km upstream   =&gt; 78/(10+x) = 42/(10−x)   =&gt; 26/(10+x) = 14/(10−x)   =&gt;13/(10+x) = 7/(10−x)   =&gt;130 − 13x = 70 + 7x   =&gt;20x = 60   =&gt; x = 3 km/hr   3 km/hrnswer : Option 3 km/hr
<result>A</result>
The speed of a boat in still water is 10 km/hr. If it can travel 78 km downstream and 42 km upstream in the same time, the speed of the stream is