1973 AMC 12 Problem 2

Attempt Problem 2 of the 1973 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 1973 AMC 12 solutions, or check the answer key.

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

2.

One thousand unit cubes are fastened together to form a large cube with edge length 1010 units; this is painted and then separated into the original cubes. The number of these unit cubes which have at least one face painted is
600600
520520
488488
480480
400400
Answer: C
Concepts:cube geometrycomplementary counting
Small hint:
Count the cubes with no painted face instead
Big hint:
Removing the outer layer leaves an 8×8×88\times8\times8 cube
Solution:
The unpainted cubes are precisely the interior 8×8×88\times8\times8 cube. Therefore the number having at least one painted face is 103−83=1000−512=488. 10^3-8^3=1000-512=488.
Therefore, the correct answer is C.
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