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average speed of train puzzle
A train is going at a speed of 60kmph towards Delhi and returned back at a speed of 30kmph. What is its average speed?
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We will go with this simple formula to calculate average speed of the train
Average Speed = (Total Distance/Time Taken);
Lets assume the distance traveled by train in one direction is x, and time taken while going towards delhi is t1, while it took t2 time while coming back from Delhi.
We can say
x/t1 = 60
x/t2 = 30
Total Average speed = 2x/(t1 + t2)
average speed = 2x /(x/60+x/30) = (2x/90x)*60*30 = 40
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40KMPH
Let the distance between Place to Delhi be X.
So the total distance distance = X+X = 2X
Now time taken for first travel from A to Delhi = X/60 hours
Time taken while coming from Delhi to A = X/30 hours
Total time taken for the to and fro journey = (X/60) + (X/30) hours = (3X/60) hours
Average speed = Total Distance / Total Time
= (2X) / (3X/60) KMPH
This gives X = 40 KMPH
Answer = 40KMPH
40 kmph using formula 2xy/(x+y)
45 kmph
40kmph