2014 AMC 8

Complete problem set with solutions and individual problem pages

Problem 19 Hard

A cube with 3-inch edges is to be constructed from 27 smaller cubes with 1-inch edges. Twenty-one of the cubes are colored red and 6 are colored white. If the 3-inch cube is constructed to have the smallest possible white surface area showing, what fraction of the surface area is white?

  • A.

    \frac{5}{54}

  • B.

    \frac 19

  • C.

    \frac {5}{27}

  • D.

    \frac 29

  • E.

    \frac 13

Answer:A

For the least possible surface area that is white, we should have 1 cube in the center, and the other 5 with only 1 face exposed. This gives 5 square inches of white, surface area. Since the cube has a surface area of 54 square inches, our answer is \boxed{\textbf{(A) }\frac{5}{54}}.