Question

a train travels 40 km at a uniform speed of 30 km/h-1. Its average speed after traveling another 40 km is 45 km h-1 for the whole journey . Its speed in the second half of the journey is a.45km h-1. b.90km h-1. c.60km h-1. d.None of these​

Answer 1

Answer:

Answer: B

Explanation:

Given:

Total distance =80km

Average speed of entire journey=45km/h

Total Time taken =total distance/average speed

=80/45 hour

Case :1

Let us CALCULATE time taken to cover first 40km

Speed=30km/h

Distance=40km

T=distance/ speed=40/30

=4/3 hr -----equation ( 1)

Case: 2

Let us CALCULATE time taken to travel next 40km

Let speed be =Xkm/ h

X=40KM/t

t=40/X hours ----equation( 2)

Total time = add equation 1 and 2

=4/3 +40/x

Since total time =80/45 hr

80/45=4/3+40/x

80/45=4x+120/3x

3x(80)=45(4x+120)

80x=15(4x+120)

80x=60x+15*120

20x=15*120

x=15*120/20

X=90km/hr

Therefore bus should travel next 40km distance at a speed of 90 km/h.

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