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
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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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