Question

which minimum number should be added to make 280 a perfect square

Answer 1

If one considers 1 the smallest (positive) perfect square, one should add -279 to 280 to get 1. If one considers 0 as a perfect square, one should add -280 to 280 to get 0. The perfect square just bigger than 280 is289 . Therefore, the required minimum number is 9.

Answer 2

9 should be added

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Hope it helps