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1989 AJHSME Problems/Problem 23

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Problem

An artist has 14 cubes, each with an edge of 1 meter. She stands them on the ground to form a sculpture as shown. She then paints the exposed surface of the sculpture. How many square meters does she paint?

\text{(A)}\ 21 \qquad \text{(B)}\ 24 \qquad \text{(C)}\ 33 \qquad \text{(D)}\ 37 \qquad \text{(E)}\ 42

draw((0,0)--(2.35,-.15)--(2.44,.81)--(.09,.96)--cycle);draw((.783333333,-.05)--(.873333333,.91)--(1.135,1.135));draw((1.56666...

Solution

We can consider the contributions of the sides of the three layers and the tops of the layers separately.

Layer n (counting from the top starting at 1) has 4 side faces each with n unit squares, so the sides of the pyramid contribute 4+8+12=24 for the surface area.

The tops of the layers when combined form the same arrangement of unit cubes as the bottom of the pyramid, which is a 3\times 3 square, hence this contributes 9 for the surface area.

Thus, the artist paints 24+9=33 \rightarrow \boxed{\text{C}} square meters.

Solution

1989 AJHSME (ProblemsResources)
Preceded by
Problem 22
Followed by
Problem 24
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Looking for a challenging geometry text? Preparing for MATHCOUNTS or the AMC exams? Check out Art of Problem Solving's Introduction to Geometry by Richard Rusczyk.
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