Question

pls solve quickly!: It took a boat 2 hours to reach town A going upstream. The way back was 1h20 min. What is the speed of the boat in still water if the speed of the stream is 3 mph?

Answer 1

Answer:

15 mph

Step-by-step explanation:

Given: Boat took 2 hours to reach Town A going upstream.

           Speed of stream= 3 mph

           Time taken to reach back home= 1 hours 20 minutes

Lets assume distance covered one side be "d" and speed of boat in still water be "s".

∴ Speed of boat in upstream= $(s-3) \ mph$

   Speed of boat in downstream= $(s+3)\ mph$

Also converting into fraction of time taken to reach back home.

Remember; 1 hour= 60 minutes

∴ Time taken to reach back home= $60+20= 80\ minutes$

Converting time given into fraction= $\frac{80\ minutes}{60\ minutes} = \frac{4}{3} \ hours$

hence, Time taken to reach back home is $\frac{4}{3} \ hours$

Now forming equation of boat travelling upstream and downstream, considering distance remain constant.

We know, $Distance= speed \times time$

⇒ $(s-3)\times 2= (s+3)\times \frac{4}{3}$

Using distributive property of multiplication

⇒$2s-6= \frac{4}{3}s +4$

subtracting both side by $\frac{4}{3} s$

⇒$2s-\frac{4}{3} s-6= 4$

Adding both side by 6

⇒ $2s-\frac{4}{3} s= 10$

taking LCD as 3

⇒ $\frac{2}{3} s= 10$

Multiplying both side by $\frac{3}{2}$

⇒$s= \frac{3}{2} \times 10$

∴s= 15 mph

Hence, 15 mph is the speed of the boat in still water.