What is the sum of the numbers in the series? 15 plus 11 plus 7 plus dot dot dot plus negative 129

The series is arithmetic, decreasing by 4 each time. From 15 to −129 is a change of −144, which takes 36 steps of −4, so there are 37 terms. The sum is 37 × (15 + (−129)) ÷ 2 = 37 × (−57) = −2,109, choice A.

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