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69:9. Abus traveling along a straight highway covers one-third of the total distance between two places with avelocity 20 km h-. The remaining part of the dis-tance was covered with a velocity of 30 km h- forthe first half of the remaining time and with velocity50 km h- for the next half of the time. Find theaverage velocity of the bus for its whole journey. |
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Answer» Let distance be xx/3 at 20 kmphremaining 2x/31/2 of remaining is 1/2 of 2x/3 = x/3 at 30 kmphand remaining ( x - x/3 - x/3 = x/3) at 50 kmphfirst part takes (x/3)/20 hours2nd part takes (x/3)/30 hours3rd part takes (x/3)/50 hoursTotally time taken for a distance of x km = (x/3) ( 1/20 + 1/30 + 1/50) hoursTotally time taken for a distance of x km = (x/30)( 15 + 10 + 6)/30 = (x/30)(31/30) = 31x/900 Average speed = total distance/total time = x/ ( 31x/900) = 900/31 kmph = 29.03 kmph |
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