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2015-05-04T03:24:17+05:30

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Distance = S  in km
speed = v  in kmph
time duration = T in hrs

             S = v T    at his normal speed.    --- (1)

if the man moves 3 kmph faster:
             T - 40/60  =  v T / (v +3)
               =>       v t - 2 v / 3 + 3 T - 2  = v T
                =>       9 T = 2 v + 6        --- (2)

if the man moves  2 kmph slower,
             T + 40/60  = v T / (v - 2)   
                 =>  v T + 2 v /3  - 2 T - 4/3  = v T
                 =>  6 T = 2 v -  4                  --- (3)

         do (2) - (3)  ,      3 T = 10    =>  T = 10/3  hours
                     =>  6 T = 20 = 2 v - 4
                   =>  v =  12  kmph

distance = S = v T =  12 * 10/3  = 40 km

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