A boat covers a certain distance downstream in 1 hour, while it comes back in 1.30 hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?	Choose the correct choice from the following answers
A) 10  B) 13  C) 11  D) 08  E) 15
Let the speed of the water in still water =x   Given that speed of the stream = 3 kmph   Speed downstream =(x+3) kmph   Speed upstream =(x−3) kmph   He travels a certain distance downstream in 1 hour and come back in 1 1⁄2 hour.   i.e., distance travelled downstream in 1 hour = distance travelled upstream in 1 1⁄2 hour   Since distance = speed × time, we have   (x+3)×1=(x−3)3/2   ⇒2(x+3)=3(x−3)   ⇒2x+6=3x−9   ⇒x=6+9= 
<gadget id="calculator">6+9</gadget>
<output>15</output>
15 kmph   Answer is 15.
<result>E</result>
A boat covers a certain distance downstream in 1 hour, while it comes back in 1.30 hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?