Answer:
Explanation:
-1+2 = 1
-3+4 = 1
-5+6 = 1
and so on till -999+1000 = 1
1 .... 1000 - these are 1000 numbers, so
1000:2 = 500 pairs with sum equal 1
4(500•1) = 4•500 = 2000
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