Question

A boat covers 16 kin in 2 hours downstream and takes 4 hours to cover the same distance upstream
How long will it take to cover 80 km in still water?
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Answer 1

Answer:

Let,

Vb = velocity of the boat in still water

Vr = velocity of the river

So, net velocity while moving downstream

= Vb + Vr

Given, Vb + Vr = 16 km/2 hr = 8 km/hr ———————(1)

Net velocity while moving upstream

= Vb - Vr

Given, Vb - Vr = 16 km/4 hr = 4 km/hr ———————(2)

Adding, (1) and (2),

We get, 2 * Vb = 12 km/hr

or, Vb = 6 km/hr

So, velocity of boat in still water is 6 km/hr.

Answer 2

Answer:

Downstream speed = 16/2 = 8 kmph

Upstream speed = 16/4 = 4 kmph

Speed of boat = (DS + US)/2 = (8 + 4)/2 = 6 kmph.

As additional infornation :

Speed of stream = (DS - US)/2 = (8 - 4)/2 = 2