Answer:
[tex]1190[/tex]
Step-by-step explanation:
[tex]a1 = 12 \\ a2 = 17 \\ d = a2 - a1 = 17 - 12 = 5 \\ d = 5 \\ l = 107 \\ [/tex]
[tex]a _{n} = l = 107[/tex]
[tex]a _{n} = a + (n - 1) \times d \\ 107 = 12 + (n - 1) \times 5 \\ 107 = 12 + 5n - 5 \\ 107 + 5 - 12 = 5n \\ 100 = 5n \\ 5n = 100 \\ \\ n = \frac{100}{5} = 20 \\ \\ n = 20[/tex]
now, sum of total numbers
[tex]S _{n} = \frac{n}{2} (a + l) \\ \\ S _{20} = \frac{20}{2} (12 + 107) \\ \\ S _{20} = 10(119) \\ S _{20} = 10 \times 119 \\ S _{20} = 1190[/tex]
