Find the value of the expression (-101) + 102 + (-103) + 104 + ... + (-199) + 200.

Examine the series in consecutive pairs.

-101 + 102 = 1

-103 + 104 = 1

-199 + 200 = 1

The second number of the pairs go from 102 to 200 so there are (200 - 102) / 2 + 1 = 49 + 1 = 50 pairs

Answer = the value is 1 * 50 = 50