Question

A train covers a distance of 90 km with a speed of 120 km per hour and covers another a distance of 40 km with a speed of 60 km per hour find its average speed.​

Answer 1

Answer:

Let original speed =xkm/hr

⇒ Time taken to travel =

x

90

hr

⇒ New speed =(x+15)km/hr

⇒ Time taken to travel =

x+15

90

hr

∴

x

90

=

x+15

90

+

2

1

⇒

x

90

−

x+15

90

=

2

1

⇒ 90(

x

1

−

x+15

1

)=

2

1

⇒

x(x+15)

x+15−x

=

180

1

⇒ 15×180=x(x+15)

⇒ 2700=x

2

+15x

⇒ x

2

+15x−2700=0

⇒ x

2

+60x−45x−2700=0

⇒ x(x+60)−45(x+60)=0

⇒ (x+60)(x−45)=0

Speed can not be negative.

∴ The original speed of the train is 45km/hr