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This block of 18 cubes, two layers high, is painted on its top and four sides but not underneath. When the cubes are separated, how many have no paint?

Competition practiceDice & Cubes
  • A0
  • B1
  • C9
  • D2

Step-by-Step Solution

A cube escapes the paint only if it is in the bottom layer (away from the top) and away from all four sides. In the bottom layer of 9 only the centre cube qualifies: 1. (0 forgets that the base is unpainted.)
Answer: B) 1

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