Question

a train covers a distance of 15 km while moving a distance 90 km/h​

Answer 1

Let the original speed of the train be xkmphr

∴ time take to cover a distance of 90km=

x

90

hrs.

The new speed of the train=x+15kmph

∴ new time taken to cover 90km=

x+15

90

hrs.

Since the train takes 30 minutes

⇒

x

90

−

x+15

90

=

2

1

⇒90(

x

2

+15x

x+15−x

)=

2

1

⇒90(

x

2

+15x

15

)=

2

1

⇒2700−x

2

−15x=0

⇒x

2

+15x−2700=0

⇒(x+60)(x−45)=0

∴x=−60 or x=45 but x cannot be negative.

∴x=45

Hence the original speed of the train =45kmph