Question

A fast train takes 3 hours less than a slow train for a journey of 600kms. If the speed of the slow train is 1 Okm/ hr less than the fast train, find the speed of the fast train. 

Answer 1

Let the speed of the slow train be S, Hence speed of the fast train = S+ 10. 

D=600Km, Time = Distance/ Speed. Time difference=3 Hours 

Hence, in these two conditions,

`600/"s" - 600/("s"  + 10) = 3`

⇒ 600 x (s+ 10) - 600 x S= S x (S+ 10) x 3 

⇒ 3s² + 305 - 6000 = 0 

⇒ S²+ 10S - 2000 = 0 

⇒ S² +5O S - 40 s - 2000 = 0 

⇒ S (S + 50)- 40 (S + 50 ) = 0 

⇒ (S +5O ) (S - 40) = 0 

As the speed can't be negative, S=40 km/ hr 

Hence, speed of the fast train = 40+ 10 = 50 km/ hr