Chapter 11 - Further Topics in Algebra - 11.2 Arithmetic Sequences and Series - 11.2 Exercises - Page 1025: 52

$${S_{10}} = - 46.25$$

$$\eqalign{ & {a_1} = - 8,\,\,\,\,{a_{10}} = - 1.25 \cr & {\text{Use the formula }}{S_n} = \frac{n}{2}\left( {{a_1} + {a_n}} \right).{\text{ Then}} \cr & {S_{10}} = \frac{{10}}{2}\left( {{a_1} + {a_{10}}} \right) \cr & {S_{10}} = 5\left( { - 8 - 1.25} \right) \cr & {S_{10}} = - 46.25 \cr} $$