Question

An ordinary train takes 3 hours less for a j ourney of 360kms when its speed is increased by 1 Okm/ hr.Fnd the usual speed of the train. 

Answer 1

Let the usual speed of the train be S, Hence speed of the train when speed is increased= S+ l O. 

D=360Km, Time = Distance/ Speed. Time difference=3 Hours 

Hence, in these two conditions , 

`360/"s" - 360/("s"  + 10) = 3` 

⇒ 360 x (s+ 10) - 360 x S = S x (S+ 10) x 3 

⇒ 3S² + 30 S - 3600=0 

⇒ S²+ 10S - 1200 = 0 

⇒ S² + 40 S -30 S -1200 = 0 

⇒ S (S + 40) - 30 (S + 40) = 0 

⇒ (S + 40) (S - 30) = 0 

As the speed can't be negative, S = 30km/ hr