Question

Ritu can row down stream 20 k. In 2 hrs and up stream 4km in 2 hrs find her speed of rowing in still water and the speed of the current

Answer 1

Let the speed of the boat in still water be xkmhr and speed of the stream be ykmhr.

Then the speed of the boat downstream = (x+y)kmhr,

The speed of the boat upstream = (x–y)kmhr

Also, Speed=(distance)(time)

In first case Ritu goes 20Km in downstream in 2hr

∴x+y=202

⇒x+y=10.....(1)

In the other case Ritu goes 4km in upstream in 2hr

∴x−y=42

⇒x−y=2.....(2)

Solving the equations by elimination method.

Adding (1) and (2) we get 2x=12⇒x=6

Substituting in one of the equation we get 6+y=10⇒y=4

Hence speed of rowing in still water is 6kmhr and the speed of the current is 4kmhr