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Printjmc
counting and probability junior
Problem
The diagram represents a -foot-by--foot floor that is tiled with -square-foot black tiles and white tiles. Notice that the corners have white tiles. If a -foot-by--foot floor is to be tiled in the same manner, how many white tiles will be needed? 
(A)
(B)
(C)
(D)
Solution
In a -foot-by--foot floor, there is white tile. In a -by-, there are . Continuing on, you can deduce the positive odd integer floor has white tiles. is the odd integer, so there are white tiles.
Final answer
C