This is an Arithmetic sequence because there is a common difference between the numbers -1: -7: -13: -19: Therefore d= -6

Use the formula for the *sum of* an arithmetic sequence:

`S 10 = n/2 ( 2a + (n - 1)d`

`S10 = 10/2(2(-1) + (10 - 1) ( -6))`

```S10 = 5 (-2 + (9) ( -6))`

```S10 = 5(-2 + (- 54)`

`` `S10 = 5 ( -56)`

``**Therefore **** S10 = -280 **

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