Respuesta :

00DEADPOOL00

Answer : 840

1 + 41 = 42

2 + 40 = 42

___________

20 pairs

20 × 42 = 840

unicorn3125

Answer:

              [tex]\bold{S_{40}=820}[/tex]

Step-by-step explanation:

[tex]1+2+3+4+ ... +40=S_{40}\\\\a_1=1\\a_{40}=40\\n=40\\\\S_n=\dfrac{a_1+a_n}2\cdot n\\\\S_{40}=\dfrac{1+40}2\cdot40=41\cdot20=820[/tex]