Answer:
[tex]S _{20} = 2150[/tex]
Step-by-step explanation:
[tex]a _{1} = 3 \\ a _{2} = 14 \\ d = a _{2} - a_{1} = 14 - 3 = 11 \\ n = 20[/tex]
[tex]S _{n} = \frac{n}{2} (2a + (n - 1)d) \\ \\ S _{20} = \frac{20}{2} (2(3) + (20 - 1) \times 11) \\ \\ S _{20} = 10 \times (6 + 19 \times 11) \\ S _{20} = 10 \times (6 + 209) \\ S _{20} = 10 \times 215 \\ S _{20} = 2150[/tex]
