### Home > PC3 > Chapter 13 > Lesson 13.2.3 > Problem13-93

13-93.

Use summation notation to write each sum. Then evaluate the sum if it exists.

1. $5+15+$$25+\dots+215$

This is an arithmetic series with a first term of $5$ and a common difference of $10$.
How many terms are in the series? This information is needed to calculate the sum.

2. $2+\frac{1}{2}+$$\frac{1}{8}+\ldots+\frac{1}{512}$

This is a geometric series with a first term of $2$ and a common ratio of $0.25$.
How many terms are in the series? This information is needed to calculate the sum.

3. $3−4+$$\frac{16}{3}-\frac{64}{9}+\ldots$

This is an infinite geometric series. What is the common ratio? How does this affect the sum?