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"Yes, when I take my dog for a walk," said a
mathematical friend, "he frequently supplies me with
some interesting puzzle to solve. One day, for example, he
waited, as I left the door, to see which way I should go,
and when I started he raced along to the end of the road,
immediately returning to me; again racing to the end of
the road and again returning. He did this four times in
all, at a uniform speed, and then ran at my side the
remaining distance, which according to my paces measured
27 yards. I afterwards measured the distance from my door
to the end of the road and found it to be 625 feet. Now,
if I walk 4 miles per hour, what is the speed of my dog
when racing to and fro?"
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