Home > PC3 > Chapter 13 > Lesson 13.2.1 > Problem13-65

13-65.

The seventh term of an arithmetic series is $−3.2$ and the twelfth term is $2.9$. What is the sum of the first $25$ terms of the series?

Solve the following system of equations to determine the first term and the common difference.

$−3.2 = a + d\left(7 − 1\right)$
$2.9 = a + d\left(12 − 1\right)$