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Malaysia IMONST 1 Senior P1

Source:

September 18, 2020
arithmeticsumsIMONST

Problem Statement

Find the value of +1+2+3−4−5−6+7+8+9−10−11−12+⋯−2020,+1+2+3-4-5-6+7+8+9-10-11-12+\cdots -2020, where the sign alternates between ++ and −- after every three numbers.
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