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The number of pairs \((x, y)\) of integers satisfying the inequality \(|x - 5| + |y - 5| \leq 6\) is:

Question and options

The number of pairs (x,y)(x, y) of integers satisfying the inequality ∣x−5∣+∣y−5∣≤6|x - 5| + |y - 5| \leq 6 is:
  1. 85
  2. 84
  3. 61
  4. 169

Answer and explanation

Correct answer: A - 85

There are 85 integer pairs. Translating the centre to (5,5)(5,5), there is one pair at distance zero under the sum of absolute differences and 4d4d pairs at each integer distance d=1,…,6d=1,\ldots,6. The total is 1+4(1+2+3+4+5+6)=851+4(1+2+3+4+5+6)=85, and omitting the centre gives 84.

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