Answer:
any of {128, 133, 140, 160, 224, 320, 380, 700, 1024}
1024 if the original grid was square
Explanation:
You want to know how many grid squares are on a piece of graph paper if a square number of grid squares can be cut from it to leave 124 grid squares.
Square graph
If the graph is square to begin with, a square of x² can be removed from its size (x+a)² to leave 124 squares. That is ...
(x +a)² -x² = 124
(a)(2x+a) = 124
The factor pairs of 124 are ...
124 = 1·124 = 2·62 = 4·31
Of these, only 2 and 62 differ by an even number, so we have a=2 and x=30.
The graph paper could be 32 units square originally, having 1024 grid squares.
Rectangular graph
There is nothing in the problem statement that requires the original graph paper be square. If it is not necessarily square, there are 13 possible shapes it could be. Those have 9 different possibilities for numbers of grid squares.
The graph paper could have originally had this number of grid squares:
- 128 = 4×32 = 8×16. The square removed is 2².
- 133 = 7×19. The square removed is 3².
- 140 = 5×28 = 7×20 = 10×14. The square removed is 4².
- 160 = 8×20 = 10×16. The square removed is 6².
- 224 = 14×16. The square removed is 10².
- 320 = 16×20. The square removed is 14².
- 380 = 19×20. The square removed is 16².
- 700 = 25×28. The square removed is 24².
- 1024 = 32×32. The square removed is 30². . . . . discussed above
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Additional comment
You may notice that removing a 24×24 square from a graph that is 25×28 leaves no border on one side.
These values were found using a search script.
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