Aboat goes 50 km downstream in the same time that it takes to go 30 km upstream. the speed of the stream is 3km/hour. find the speed of the boat in still water.

12 km/h

Step-by-step explanation:

Given: Distance covered by boat downstream = 50 km

           Distance covered by boat upstream = 30 km

           Time taken by boat in down stream and upstream are equal.

           Speed of the stream = 3 km/h

Let x be the speed of boat in still water.

∴ Speed of boat in downstream =

Speed of boat in upstream =

As we know,

And time remain same for both upstream and downstream

∴

Now, cross multiply both side

⇒  

⇒

∴

∴ Speed of boat in still water is 12 km/h

1) is right

step-by-step explanation: