Distance between two stations a and b is 778km. A train covers the journey from a to b at 84 km per hour and returns back to a with a uniform speed of 56 km per hour. Find the average speed of train during the whole journey. 60 km/hr 30.5 km/hr 57 km/hr 67.2 km/hr
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From a to b,
Distance=778km
speed=84km/hr
time= distance÷speed
=778÷84
=9.25hr
From b to a,
Distance=778km
speed=56km/hr
time=distance÷speed
=778÷56
=13.89hr
Av.speed=total distance÷total
time
=778+778÷9.25+13.89
=67.2km/hr
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