In a hollow integer grid, every row and column of the border must add up to the same 'border sum'. The top row is 4, −6, 5 (sum 3). The bottom row is x, −2, 1. What must x be for the bottom row to also sum to 3?
- A.2
- B.3
- C.4 ✓
- D.5
Explanation: x + (−2) + 1 = 3, so x − 1 = 3, giving x = 4.
Class 6 IMO Mathematics Olympiad practice · Number Sense · Integers — The Other Side of Zero
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