Aptitude - Boats and Streams - Discussion

I agree that the answer will be 1 hour 25 min.

@All.

It's very simple.

Speed of the downstream S = D/T.
D= 1km,
T = 10mint, mint convert to hour.
10/60 hour then,

S = 1km / (10/60)hr,
= 60/10 km/hr.

Downstream speed s = 6 km/hr then,
Upstream speed S = D/T.
= 2km / 1hr = 2km / hr.
Speed in still water = 1/2 ( Down S + Up S )
1/2 ( 6+2 ) = 4km / hr.

So we need T? For stationary water, D is given 5km ...
Then Speed in still water = 4km /hr.

T = D / S = 5/ 4
= 1 1/4 hours.
= 1hr 15 mint.

@Kessy

Simply need to find the speed of the boat.
You have downstream and upstream speed and,
Downstream speed=Speed of boat +Speed of stream.

6=x+y---------> 1
Upstream speed=Speed of boat-Speed of stream

4=x-y------------> 2

Solve both 1&2 equations and get x that is the speed of the boat.

Anyone, please explain this step 1/2 times (6 + 2).

Thanks @Mayur.

Please discuss the proper way to find required time.

I also agree, The answer should be 1h and 25 mins.

Speed = Distance /Time.

Upstream Speed = 2/1 = 2 km/hr.
Downstream Speed = 1KM/10Min = 1/(10/60)hr = 1/(1/6) Km/Hr = 6 Km/Hr.

Now, Speed in Still Water = 1/2 (a+b)
a = Upstream speed means the speed of the boat against the current of the stream.
b. = Downstream speed means boat speed along the stream
= 1/2(2+6) after simplifying and is 4 Km/hr.

Total time required to travel distance of 5km for a boat in stationary water will be?

Time = Distance / Speed ----> Formula.

= 5/4 -> 4 km/hr is the speed of the boat in stationary water & 5 Km be the distance.
= 1.25 hr => 1 hr 15 min.
25/100 *60 = 15 for a minute to hour conversation.

Thank you @Sonia.

1hr = 60mins.

So, 1/4 of 1 hr = 1/4*60= 15min.