Question

Ramu can row downstream
20km in 2 hours, and the upstream 4km
in 2 hours. What will be the speed of
rowing in still water?​

Answer 1

Given:

For downstream:

The distance traveled = 20 km

Time = 2 hours

For upstream:

The distance traveled = 4 km

Time = 2 hours

To find:

The speed of rowing in still water

Solution:

We know that,

Let the speed of the boat in still water be "x" km/hr and speed of the stream be "y" km/hr, then

Speed downstream = (x + y) km/hr

Speed upstream = (x - y) km/hr

Also we have the formula, $Speed$ = $\frac{Distance}{Time}$

According to the question and using the formula, we can form equations as,

Speed downstream = (x + y)

⇒ $\frac{20}{2}$ = $(x + y)$

⇒ $\bold{(x + y) = 10}$ ........ (i)

and

Speed upstream = (x - y)

⇒ $\frac{4}{2}$ = $(x - y)$

⇒ $\bold{(x - y) = 2}$ ........ (ii)

Now, adding equation (i) & (ii), we get

x + y = 10

x - y =   2

------------------

2x = 12

-----------------

∴ x = $\frac{12}{2}$ = 6 km/hr

Thus, the speed of  rowing in still water is 6 km/hr.

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