Question

A train travels at a certain average speed for a distance of 120 km and then travels a distance of 130 km at an average speed of 5 km/hr more than its original speed. If it takes 4 hours to complete the total journey, then average speed of train during 130km journey and if original speed is decreased by 10 km/hr and is constant in whole journey, then the. time taken. by the train to complete the journey is?​

Answer 1

Answer:

42 km/h

Step-by-step explanation:

Let, the original average speed be x km/hr.

Time taken at a speed of x km/hr (t

1

)=

x

63

hrs

Time taken at a speed of x+6 km/hr (t

2

)=

x+6

72

hrs

t

1

+t

2

=3

x

63

+

x+6

72

=3

⟹

x(x+6)

63((x+6)+72x

=3

⟹63x+378+72x=3x(x+6)

⟹378+135x=3x

2

+18x

⟹3x

2

+18x−135x−378=0

⟹3x

2

−117x−378=0

⟹3(x

2

−39x−126)=0

⟹x

2

−39x−126=0

⟹x

2

−42x+3x−126=0

⟹x(x−42)+3(x−42)=0

⟹(x−42)(x+3)=0

Either x=42 or x=−3

∵ speed cannot be negative. x=42 is considered.