SOLUTION: A train goes from New Orleans to Boston at 40 mph. On the way back it returns with a speed of 80 miles per hour. If it takes less time to return, what is it's average speed?

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Question 980522: A train goes from New Orleans to Boston at 40 mph. On the way back it returns with a speed of 80 miles per hour. If it takes less time to return, what is it's average speed?
Found 2 solutions by ikleyn, Alan3354:
Answer by ikleyn(52800) About Me  (Show Source):
You can put this solution on YOUR website!

The train spends  L%2F40  hours to go from New Orleans to Boston.
It spends  L%2F80  hours to go from Boston to New Orleans.

So,  the train spends  L%2F40+%2B+L%2F80 = 2L%2F80+%2B+L%2F80 = 3L%2F80  hours for the way from New Orleans to Boston and back.

Hence,  the average speed for this trip is the full distance  (which is 2L)  divided by the full time  3L%2F80,  i.e.

2L%2F%28%283L%2F80%29%29 = 2L%2A80%2F%283L%29 = 160%2F3 = 53.333 mi%2Fh.

Answer.  The average speed was  53.333 mi%2Fh.


Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
A train goes from New Orleans to Boston at 40 mph. On the way back it returns with a speed of 80 miles per hour. If it takes less time to return, what is it's [sic] average speed?
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If it takes less time... ? It's going 2x as fast, takes half as long, no if about it.
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Avg speed of a round trip = 2*r1*r2/(r1+r2)
= 2*40*80/(120)
= 160/3 mi/hr
= 53.33 mi/hr
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it's = it is