Solution #44: House of Cards

Note first that in all houses of cards, every level has three cards more than the level immediately above it.

The number of cards for a 47-story house is therefore

   2
 + 2 + 3
 + 2 + 3.2
 + 2 + 3.3
 + ...
 + 2 + 3.(n-1)
 + ...
 + 2 + 3.(47-1)
----------------------
47.2 + 46.47/2 x 3 = 3337

Source: Berrondom, Marie
Categories: Number sense, Arithmetic
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