Aptitude - Boats and Streams - Discussion

In the question they given the data that

speed of boat 13 km/hr and speed of stream is 4 km/hr

and they asked us to solve the time taken by the boat in down stream for a distance of 68 kms.

we know as per the formula down stream means speed of boat + speed of stream

therefore,
down stream = 13+4=17 km/hr
as per the problem we got to find time taken by boat to travel a distance of 68km down stream.

we have formula that, time=distance/speed
=68/17
=4 hours

Thanks Balaji.

Thanks for your explanation.

Total speed during downstream,
Speed = 13kmph + 4 kmph = 17 kmph.
Time = distance / speed = 4 hours.
Hope this helps!

Speed of boat in still water = 13km/hr.
Speed of the stream = 4km/hr.
Time taken by the boat to go 68 km downstream = ?

Speed of boat in downstream = (13+4)km/hr.
= 17km/hr.

Time = distance/speed.
= 68/17hr.
= 4hr.

(Total speed)downstream = Speed of boat + Speed of stream.

Time = Distance/speed.

Speed in Still water = 13 km/h.
Speed of the stream = 4 km/h.

Downstream = 13+4 = 17km (speed in Still water + speed of the stream).
Time Take = 68/17 = 4 hrs.

How to know particularly which formula to use whether downstream or upstream? Bit confusing?

It is given in the question to find time taken to go 68 km downstream.

Downstream speed = a.
Upstream speed = b.

Stream speed = 1/2 (a-b)----Formula.
Boat speed = 1/2 (a+b)-----Formula.

Given boat speed = 13.
Stream speed = 4.

So 1/2(a+b)+1/2(a-b) = 13+4.

==> a=7.

Given D = 68km.

D = S*T.
Ta = D/Sa.

=>68/17.

=>4.

So time taken by the boat to go 68 km downstream is 4 hrs.