Question

A boat travels 30 km upstream in a river in the same period of time as it takes to travel 50 km downstream. If the speed of river current is 5 km/h, find the speed of the boat in still water.​

Answer 1

Answer:

Let the speed of boat be (x−5) in upstream and (x+5) in downstream

s=

t

d

or t=

s

d

⇒

5

30

=6hours and

5

50

=10hours

then the equation will be 6(x+5)=10(x−5)

6x+30=10x−50

⇒10x−6x=30+50

⇒4x=80

⇒x=

4

80

=20

speed of the boat in still water is 20kmph

Answer 2

Step by Step explanation :

So, let the speed of the boat that we have to calculate be x.

Now, as the boat travels upstream with speed x and the rate of stream is 5 kmph, we will have-

Speed of boat in upstream: (x−5)

As the boat travels downstream with speed x and the rate of stream is 5 kmph, we will have-

Speed of boat in downstream: (x+5)

Now, as we all know the formula of speed is-

speed=dt (Where d stands for distance and t stands for time)

So, from above formula, the formula for time will be-

t=ds (Where t stands for time, d for distance and s for speed)

Now, as the time period is given same, we will have:

ds (for upstream) = ds (for downstream)

⇒30x−5=50x+5⇒3x+15=5x−25⇒15+25=5x−3x⇒40=2x⇒x=20

Thus, the speed of the boat is 20 kmph.