The current of stream runs at 1kmph. A motor baot goes 35km
upstream and back again to the starting point in 12hours. The speed of the
motor boat in still water is
8km/hr
3km/hr
6km/hr
5km/hr
Explanation:
Let the speed of the motor boat in still water be x kmph then.
Speed downstream = x+1 km/hr
Speed upstream = x-1 km/hr
35/x+1 + 35/x-1 = 12
x-1+x+1/ (x+1) (x-1) = 12/35 == > 2x / x2 – 1 = 12/35
= 6x2 – 35 x – 6 = 0
= 6x2 – 36 x+x – 6 = 0
= 6x (x-6) + 1 (x-6) = 0 è (6x+1) (x-6) = 0
x=6 km/hr
Let the speed of the motor boat in still water be x kmph then.
Speed downstream = x+1 km/hr
Speed upstream = x-1 km/hr
35/x+1 + 35/x-1 = 12
x-1+x+1/ (x+1) (x-1) = 12/35 == > 2x / x2 – 1 = 12/35
= 6x2 – 35 x – 6 = 0
= 6x2 – 36 x+x – 6 = 0
= 6x (x-6) + 1 (x-6) = 0 è (6x+1) (x-6) = 0
x=6 km/hr