Question 252532
Draw a diagram of a square with 25 equal squares in it. Count the squares along the 2 diagonals. There are 9. because you didn't count the central square twice.
If you add 1 and divide by 2 you get the number of squares on each side.
125+1=126 
126/2=63 tiles on a side
63^2=3969 tiles in the hall.
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Ed