Răspuns:
5203
Explicație pas cu pas:
[tex]18+19+20+...+101+102+103 =\\= 1 + 2 + 3 +... + 18 + 19+...+102+103 - 1 - 2 -3-...-17-18\\=1+2+3+...+101+102+103 -(1+2+3+...+16+17)\\=\frac{103*(103+1)}{2} -\frac{17*(17+1)}{2} \\\\=\frac{103*104 - 17 * 18}{2}\\\\=103*52 - 17 * 9\\=5356 - 153 = 5203[/tex]
