A boat covers a certain distance downstream in 4 hours but takes 6 hours to return upstream to the starting point. If the speed of the stream be 3 km/hr, find the speed of the boat in still water
Choose the correct choice from the following answers:
A) 15 km/hr
B) 12 km/hr
C) 13 km/hr
D) 14 km/hr
E) None of these
Explanation :   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 4 hour and come back in 6 hour.   ie, distance travelled downstream in 4 hour = distance travelled upstream in 6 hour   since distance = speed × time, we have   (x+3)4=(x−3)6   =&gt; (x + 3)2 = (x - 3)3   =&gt; 2x + 6 = 3x - 9   =&gt; x = 6+9= 
<gadget id="calculator">6+9</gadget>
<output>15</output>
15 kmph. 15 km/hrnswer : Option 15 km/hr
<result>A</result>
A boat covers a certain distance downstream in 4 hours but takes 6 hours to return upstream to the starting point. If the speed of the stream be 3 km/hr, find the speed of the boat in still water