A boatman can row a certain distance down the stream in 2 hours and up the stream the same distance in 3 hours. If the stream flows at the rate of 4 km /hr, What is the speed of the boat in still water ?
Solution
|
Down stream
|
upstream
|
Time:
|
2
|
3
|
Speed:
|
3
|
2
|
Now, the ratio of the speed of boat in still water : Velocity of stream
$\dfrac{(3 + 2)}{2}$ = $\dfrac{(3 - 2)}{2}$
$~~~~~~$ 5 : 1
4 × 5 = 20 km/hr. : 4 km./hr.
$\therefore$ $S_b$ = 20 km./hr.