2004 AMC 8 Problem 15

Attempt Problem 15 of the 2004 AMC 8 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2004 AMC 8 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

15.

Thirteen shaded and six unshaded hexagonal tiles were used to create the figure below. If a new figure is created by attaching a border of unshaded tiles with the same size and shape as the others, what will be the difference between the total number of unshaded tiles and the total number of shaded tiles in the new figure?
55
77
1111
1212
1818
Answer: C
Concepts:tilingpattern recognition
Small hint:
The original figure has one center tile, a ring of 6,6, and a ring of 12.12.
Big hint:
The next hexagonal border has 1818 tiles.
Solution:
The original figure has 1313 shaded tiles and 66 unshaded tiles.
The new border is the next hexagonal ring around the figure, which has 1818 unshaded tiles.
The new figure has 6+18=246+18=24 unshaded tiles and 1313 shaded tiles, so the difference is 24−13=11.24-13=11.
Thus, C is the correct answer.
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