Aptitude - Boats and Streams - Discussion

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.

@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.

Let Speed of the boat is 'u' and Speed of the Stream is 'v'.

Then u+v=6km/hr ///Speed of the boat in downstream.
Then u-v=2km/hr ////Speed of the boat in upstream.

Here we need the speed of the boat in Still Water which is 'u', because the speed of stream is zero in still water i.e;v=0.

By solving u+v =6 & u-v=2 ,we get u=4km/hr.

Ao, Speed of the boat in Stillwater is 4km/hr, then to travel 5km it take 1hr 15mins.

@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.

Upstream=2km (1 hr).

Downstream =1km (10 min).
For 10 min=1 km.
For 1 hr = 6 km.

Speed in still water = 1 /2(a + b) km/hr.

Speed of still water = 1/2(2+6).
= 1/2(8).
= 4km/hr.

Time = distance/time.

Time taken to go 5 km in stationary water = (5/4).

= 1hr 25min.

We can do this question by another way.
Let us suppose speed od boat is we and speed of stream is v1.
When boat against the current then speed =v-v1.
And when boat along the current then speed =v+v1.

v-v1=2/1;.
v+v1=1/ (10/60).

Calculate the value of v.
I got value of v 4km/h.
T=5/4.

T=1 hr 15 min.

We know that,

Upstream speed = u-v;
Downstream speed=u+v;.

According to formula, s=d/t.

u-v = 2/1, and

u+v = 60/10.

On solving these equations, we get.

u=4 and v=2.

Therefore, speed of boatman = 4 km/hr.

Hence, t=d/s.

t=5/4.

We get 1hr 15min is answer.

I am still confuse for conversion of time. Please somebody can help me to understand all types of conversion of time.

Here they have divided in some problem they have multiplied it.

Here, 3/10*60 and in one example 18*12/60, why like this?

See here.

Since downstream = 1km (10mins).
So for 10 mins = 1km.

So from this when we convert to hrs we get.
10/60 =1 km.

And that 60 goes to rhs it will be multiplied with kms.
i.e., 10=1*60.

So 1 hr = 6 kms.

The question says a boatman goes 2 km against the current of the stream in 1 hour which means upstream so, it is 2km/hr.