[tex]100 + 101 + 102 + ... + 200 = (1 + 2 + 3 + ... + 200) - (1 + 2 + 3 + ... + 99) = \frac{200 \cdot201}{2} - \frac{99 \cdot100}{2} = 100 \cdot201 - 99 \cdot50 = 20100 - 4950 = \boxed{ \bold{15150}}[/tex]
