Question

What is the sum of ten terms of a finite arithmetic series if the first term is 13 and the last term is 89?

Answer 1

Formula for the sum of n terms of a finite arithmetic series is

$S_n=\dfrac{a_1+a_n}{2}\cdot n.$

If $n=10,\ a_1=13,\ a_{10}=89,$ then

$S_{10}=\dfrac{13+89}{2}\cdot 10=51\cdot 10=510.$

Answer: 510.