Question

The first and last terms of a 10-term arithmetic series are listed in the table. What is the sum of the series?

Answer 1

The sum of an arithmetic series:
$S_n=\frac{n(a_1+a_n)}{2}$

$a_1=3 \\ a_{10}=75 \\ \\ S_{10}=\frac{10(a_1+a_{10})}{2}=\frac{10(3+75)}{2}=5(3+75)=5 \times 78=390$

The sum of the series is 390.