sivanarayan

• Jan 13th, 2006

 

xs = stream speed, x = boat speed.

4(x+xs) = 18

6(x-xs) = 20

x=47/12

xs=9/4

ravi

• Jan 16th, 2006

 

rate down stream=18/4 km/hr

rate up stream=20/6 km/hr

speed of current= 1/2(9/2-10/3)

                      = 7/12 kmph

Sundar

• Jan 20th, 2006

 

a=speed of the water;

b=speed of the boat;

6(b-a)=20;

4(b+a)=18;

6b-6a=20

4b+4a=18

a=speed of the water=7/12;

b=speed of the boat=47/12

krissri.2005

 Profile Answers by krissri.2005 

• Oct 14th, 2010

 

Let the velocity in still water be V and the current be U.
The net velocity upstream (against the current) is 20/6 = V - U.

The net velocity downstream is ,18/4 = V + U.
Add the equations to get 7.83 = 2V.
Subtract the equations to get, 1.17 = 2U.
So, V= 3.91 and U = .58

krissri.2005

 Profile Answers by krissri.2005 

• Oct 14th, 2010

 

Speed of boat upstream = 20/6 km
Speed of boat downstream = 18/4 km = 9/2 km = 27/6 km

Now, the current is helping the boat down stream. This makes their speed
combine. For upstream, it is basically the speed of the boat minus the speed of
the river if you think about it. This results in:

{ x + y = 27/6
{ x - y = 20/6

Adding these gives us:

x + y = 27/6
x - y = 20/6
------------------
2x = 47/6
x = 47/12

Plugging this into the top equation gives:

x + y = 27/6
==> 47/12 + y = 54/12
==> y = 7/12

Therefore, the boat's speed is 47/12 km ≈ 3.92km and the current's speed is
7/12 km ≈ 0.58km.