Question

A train travels a distance of 480 km at a uniform speed. If the speed had been
8 km/h less, then it would have taken 3 hours more to cover the same distance. We
need to find the speed of the train.
​

Answer 1

Here,

d= 480km

s/t= 480

s= 480/t (1)

Now,

New Speed = speed-8

New time= t+3

So, covering the same distance

will be given by,

D= s×t

480= (s-8)(t+3)

480= (480/t -8)(t+3)

480= (480-8t)/t ×(t+3)

480t= 480t+1440-8t²-24t

0= -8t²-24t+1440

8(t²+3t-180)=0

t²+3t-180=0

t²+15t-12t-180=0

t(t+15)-12(t+15)=0

(t-12)(t+15)= 0

either t= 12

or t= -15

Since time cannot be negative, t= 12 hr

plugging the value of t in equation (1)

s= 480km/12h

= 40km/hr