1992 AMC 12 Problem 8

Attempt Problem 8 of the 1992 AMC 12 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 1992 AMC 12 solutions, or check the answer key.

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

8.

A square floor is tiled with congruent square tiles. The tiles on the two diagonals of the floor are black. The rest of the tiles are white. If there are 101101 black tiles, then the total number of tiles is
121121
625625
676676
25002500
26012601
Answer: E
Concepts:square griddiagonalscounting overlap
Small hint:
If the floor has nn tiles on a side, count the tiles on both diagonals
Big hint:
Because the total number of black tiles is odd, the two diagonals share one center tile
Solution:
For an odd n,n, each diagonal contains nn tiles and the two diagonals share only the center tile. Hence 2n−1=101,2n-1=101, so n=51.n=51. The floor therefore contains 512=260151^2=2601 tiles.
Thus the correct answer is E.
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