Question

speed of boat in still water is 15km/h it goes 30km upstream and return back at that place back in 4hrs30min .find speed of stream?
plz explain proper answer!​

Answer 1

Answer:

5 km/hr

Step-by-step explanation:

Let's assume that the speed of stream is = x km/h

Speed of boat in still water = 15 km/h

Total time taken = 4 hour 30 mins or 9/5 hrs

Distance covered = 30 km

Then,

Speed of boat downstream =( 15 + x ) km/h

Time taken downstream = (30/15 + x ) hrs

As time = distance / speed

Speed of boat upstream = ( 15 - x ) km/h

Time taken upstream =( 30/15 - x ) hrs

Now,

Total time taken = Time taken downstream + Time taken upstream

9/2 = (30/15 + x ) + (30/15 - x )

=> 60/(15+x)  + 60/(15-x) = 9

LCD: (15+x)(15-x)

=> 60(15 - x) + 60(15 + x) = 9(15 + x)(15 - x)

=> 60(15 - x + 15 + x) = 9(225 - x²)

=> 60(30) = 2025 - 9x²

=> 9x² = 2025 - 1800

=> 9x² = 225

=> x² = 25

=> x = 5

Therefore, speed of the stream = 5 km/h

Hope it helps!