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Question A train travels 40 km at a uniform speed of 30 km/h its average speed after travelling another 40 km is 45 km/h for the whole journey, its speed in the second half of the journey isa.45 km/hb.90 km/hc.60km/hrd.30km/h |
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Answer» 90Explanation:Given:Total distance =80kmAverage SPEED of entire journey=45km/hTotal Time TAKEN =total distance/average speed=80/45 hourCase :1Let us CALCULATE time taken to COVER first 40kmSpeed=30km/hDistance=40kmT=distance/ speed=40/30=4/3 hr -----equation ( 1)Case: 2Let us CALCULATE time taken to travel next 40kmLet speed be =Xkm/ hX=40KM/tt=40/X hours ----equation( 2)Total time = ADD equation 1 and 2=4/3 +40/xSince total time =80/45 hr80/45=4/3+40/x80/45=4x+120/3x3x(80)=45(4x+120)80x=15(4x+120)80x=60x+15*12020x=15*120x=15*120/20X=90km/hrTherefore bus should travel next 40km distance at a speed of 90 km/h |
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