Question

On 120 km track , a train travel the first 30 km at uniform speed of 30km/hr .how fast must the train in next 90 km so that the average speed is 60 km for the entire trip

Answer 1

let the required speed be x

total distance=120 km
first 30 km, by 30 km/hr= 1hr
120-30=90 km
s=distance/time
   60                 =  120*x/x+90
   60 (x+90)      =  120x  
   60x + 60*90  =  120x
   60*90            =  120x-60x
   x                    =  60*90/60
   Therefore,
required speed is 90 km/hr