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It is very good problem to exercise your mind, from the age of 7 to 77.
There are 6 persons in front of Amy, and this amount of 6 is twice as many people are behind her.
Hence, there are 6/2 = 3 persons behind Amy.
Therefore, there are 6 + 1 + 3 = 10 persons in the line, in all.
The person marked by the number 1 in this expression, is Amy herself.
ANSWER. There are 10 persons in the line, in all.
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