Question

a boat is rowed down a river at21km /h and upvthe river at 9km /h .what is the speed of river?​

Answer 1

Step-by-step explanation:

Let speed of boat in still water = a km/hr

Let speed of stream = b km/hr

Then speed of boat in upstream = a – b km/hr

And speed of boat in downstream = a + b km/hr

Then,

⇒ a + b = 21

⇒ a – b = 9

Solving these 2 equations, we get,

⇒ a = 15 km/hr

Answer 2

Answer:

Please see the attachment