Question

calculate 1 - 2 + 3 - 4 + 5 - 6 + .......... + 179 - 180

Answer 1

answer would be 178

Answer 2

S =   1 - 2 + 3 - 4 + 5 - 6 + ___ + 179 - 180

+   S =       1 - 2 + 3 -  4 + 5 - 6 + ___ + 179 - 180

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2S =           1 - 1 - 1 - 1 - 1 - 1 - 1 - 1 - ___ - 1 - 1 - 1 - 180

2S = -180

S =   $\frac{-180}{2}$

S = -90