Question

A boat takes 64 mins less to travel 40km downstream than to travel the same distance upstream.if the speed of the boat is 20 km/hr the speed of the stream is

Answer 1

Let, the speed of Stream be y km/h then

Let, the time taken to go 40 km downstream be t hours

Then, the time taken to go 40 km upstream is ( t+1 ) hours....... since 60 min = 1 hr

Also,

Time = Distance/ Speed

So,

t = 40/(15+y)

t+1 = 40/(15-y)

Now,

=>40/(15-y) - 40/(15+y) = 1

=> y²+80y - 225 =0;

we get,

y= 2.72 km/h

So, the speed of the stream is 2.72 km/h

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