Question 1036256
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A train 100 meter long takes 3 second to   cross a man walking at the rate of 6km/hr in a direction opposite to that of the train. 
Find the speed of the train.
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<pre>
Let "u" be the speed of the train (in meters/minute !), now unknown.

Then the equation is

0.05*u + 100*0.05 = 100     (1)

(0.05 is the 0.05 minute = {{{1/20}}} minute = 3 sec;
100  = 6 {{{km/h}}} = {{{6000_m/60_minutes}}} = 100 {{{m/min}}} ).

Simplify and solve (1):

0.05u + 5 = 100,

0.05u = 100 - 5 = 95,

u = {{{95/0.05}}} = 1900 {{{m/min}}} = 114 {{{km/h}}}.

<U>Answer</U>.  The speed of the train is 114 {{{km/h}}}.
</pre>Solved.