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Labor Day Maths Puzzle

Labor DayLabor Day Maths Puzzle - 9 January

Manish drive to his office at 20km/hr. After reaching office, he realize that today is a holiday of 'Labor Day'.He went back at average speed of 30km/hr. Discounting the time spent in the stoppage what was his average speed of his journey ?

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  1. avg speed is= 2*d/((d/20)+(d/30))=24km/hr
    where d is distance to office

  2. 2D= Y(T2+T1) I don't understand what this means.

  3. 24kmph.
    Assume 'd' be the distance between his office and home.
    equate it with the two given speed.
    Divide it .You will get ratio of t2:t1 to be 1.5.
    Since t2 is proportional to t1 and independent of any other variable,you can assume 1 hour be the time t1 .This will not affect the actual average velocity,since it only depends on relationship between the two velocities or two times if either one of them,i.e. velocities or times are known(in this case velocity is known).
    On substituting,you will get d=30
    Total distance covered 2d=60.
    time taken=2.5
    so average speed is 24