document.write( "Question 147415: the speed of a stream is 3 km/hr. a boat travels 4 km upstream in the same time it takes to travel 10 km downstream. What is the speed of the boat in still water? \n" ); document.write( "
Algebra.Com's Answer #107787 by aswathytony(47)\"\" \"About 
You can put this solution on YOUR website!
let the speed of boat in still water is x km/hr.\r
\n" ); document.write( "\n" ); document.write( "given speed of stream is 3 km/hr.\r
\n" ); document.write( "\n" ); document.write( "then speed of boat upstream = ( x - 3) km/hr
\n" ); document.write( " speed of boat downstream = (x + 3 ) km/hr\r
\n" ); document.write( "\n" ); document.write( " Distance travelled upstream = 4 km
\n" ); document.write( " time taken to travel upstream = distance travelled upstream / speed of boat
\n" ); document.write( " upstream
\n" ); document.write( " = 4 / (x - 3 ) .............(1)\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( " Distance travelled downstream = 10 km
\n" ); document.write( "time taken to travel downstream = distance travelled downstream / speed of boat
\n" ); document.write( " downstream
\n" ); document.write( " = 10 / (x + 3) ............(2)
\n" ); document.write( "given that boat takes same time to travel upstream and downstream.i.e; (1) & (2) are equal
\n" ); document.write( " i.e. 4/(x-3) = 10/ (x + 3 )\r
\n" ); document.write( "\n" ); document.write( " 4 * (x +3 ) = 10 * (x- 3)
\n" ); document.write( " 4x + 12 = 10x - 30
\n" ); document.write( " 12 + 30 = 10x -4x
\n" ); document.write( " 42 = 6x
\n" ); document.write( " x = 42 / 6 = 7.\r
\n" ); document.write( "\n" ); document.write( "i.e speed of boat in still water is 7 km/hr. \n" ); document.write( "
\n" );