In current of a stream runs at 2 km/hr. A motor boat goes 30 km upstream and back again to the starting point in 20 hours. The speed of the moter boat in still water is: Pick one.
A) 5 km/hr	B) 8 km/hr	C) 2 km/hr	D) 4 km/hr	E) 8 km/hr
Explanation:   Let the speed ofboat in still water be x km/hr.   Speed down stream = (x + 2) km/hr   Speed up stream = (x - 2) km/hr   30/(x+2) + 30/(x-2) = 20 hours   (30x-60+30x+60)/(x2-4) = 20   60x = 20x2 - 80   3x = x2 - 4   x2-3x-4=0   x2-4x+x-4=0   x(x-4)+1(x-4)=0   x=4, x=-1   Speed of moter boat is 4 km/hr   Answer: Option 4 km/hr
<result>D</result>
In current of a stream runs at 2 km/hr. A motor boat goes 30 km upstream and back again to the starting point in 20 hours. The speed of the moter boat in still water is: