Chapter 12 - Sequences; Induction; the Binomial Theorem - 12.2 Arithmetic Sequences - 12.2 Assess Your Understanding - Page 814: 55

$15,960$

We are given the sequence: $14,16,18,20,......$ As $16-14=18-16=20-18=2$, the sequence is arithmetic. Determine its first term and common difference: $a_1=14$ $d=2$ We determine the sum of the first 120 terms using the formula: $S_n=\dfrac{n(2a_1+(n-1)d}{2}$ $S_{120}=\dfrac{120(2\cdot 14+(120-1)\cdot 2)}{2}=\dfrac{120(266)}{2}=15,960$