Question 1119414
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This is not a math problem; it is a riddle.  As such, it is good entertainment; but it is not really appropriate for this web site.<br>
What she is buying are numbers that can be used, for example, to display the address of a house on a street.  "1" requires one such number; "12" requires two; and "144" requires 3.  The numbers cost $0.50 each.