Question

what is the speed of train

Answer 1

1) distance travelled = 480 km
let the speed of the train = x km/hr
time (t1) = d/speed

t1 = 480/x -------(1)

2)
distance =480 km
speed = (x-8) km/hr

time (t2) = 480/(x-8) ------(2)

given 

t2- t1 = 3hr

480/(x-8)  -  480 / x = 3

480{ 1/(x-8) - 1/x} =3

480 { (x- (x-8)/(x-8)x } =3

480 { [x-x+8]/(x-8)x } =3

480 { 8/ (x^2 -8x) } =3

480 *8 /3 = x^2 -8x

1280 = x^2 -8x

x^2 -8x -1280=0

x*x -40x +32 x - 32*40=0

x(x-40) +32(x- 40)=0

(x-40)(x+32) =0

x-40 =0 or x+32 =0

x= 40 or x= -32

x should not be negative 
therfore
 speed of the train = x = 40 km/hr