The speed of a boat in still water is 30 kmph. What is the speed of the stream if the boat can cover 80 km downstream or 40 km upstream in the same time?	Choose the correct choice from the following choices:
A) 11 kmph B) 10 kmph C) 12 kmph D) 16 kmph E) 15 kmph
X = the speed of the stream   (30 + X) / (30 - X) = 2/1   30+ X = 60 - 2X   3X = 30   X = 10 km/hour   If the speed of the stream is 10km/hour, then the 'downstream' speed of the boat is   30+10= 
<gadget id="calculator">  30+10</gadget>
<output>40</output>
40km/hour and the 'upstream' speed of the boat is 30-10= 
<gadget id="calculator">30-10</gadget>
<output>20</output>
20km/hour. In that way, if the boat traveled for 2 hours, it would travel 2x40= 80km downstream and 2x20 = 40 km/hour upstream.   Answer : 10 kmph
<result>B</result>
The speed of a boat in still water is 30 kmph. What is the speed of the stream if the boat can cover 80 km downstream or 40 km upstream in the same time?