Question

A man can go by boat 8 km and come back within 4 hours 16 minutes . If the rivers runs at the same rate of 1 km per hour , find the speed of boat in still water

Answer 1

Answer: 4km/h

Step-by-step explanation:let the speed of boat in still water be xkm/h.

Speed of stream =1km/h

Distance = 8km

Speed during downstream = x+1

Speed during upstream =x-1

We know that , speed = distance / time

Therefore, time taken during  downstream = 8 / x+1

Time taken during upstream = 8/x-1

And total time taken = 4 hours 16min = 4+4/15= 64/15

According to the question:

8/x+1 +8/x-1 = 64/15

X= -1/4 and 4

Speed can't be negative

So, speed of boat in still water is 4km/h.

Answer 2

4km/hr

Step-by-step explanation:

Let the speed of the boat X.

The Speed of the river is 1km per hour.

So, when the boat is going with the flow then the speed will be (x+1)

And when the boat is going against the flow then the speed will be (x-1)

⇒(8/x+1)+(8/x-1)=4.267

⇒(16x/x²-1)=4.267

⇒3.75x=x²-1

⇒x=4(answer)

Hence the speed of the boat in still water will be 4km/hr.