Question

A train travels 480 km at a uniform speed. If the speed had been 10km/h more, it
would have taken 4 hours less for the same journey, find the speed of the train?​

Answer 1

D=480

s×t= 480km

s= 480km/t (1)

Now, adding 10 to speed= s+10

and reducing 4 from time= t-4

where the new equation is

480= (s+10)×(t-4)

480= (480/t +10)(t-4)

480= (480+10t)/t × (t-4)

480t= (480+10t)(t-4)

480t=480t-1920+10t²-40t

480t-480t= 10t²-40t-1920

0= 10(t²-4t-192)

t²-4t-192=0

t²-16t+12t-192= 0

t(t-16)+12(t-16)=0

(t+12)(t-16)=0

either t=-12

or t= 16

Since time cannot be negative, t= 16 hr

Now putting this value in equation (1)

s=480km/t= 480km/16hr = 30km/hr

Hence, the speed of the train is 30km/hr