### Home > PC3 > Chapter 12 > Lesson 12.1.2 > Problem12-26

12-26.

Use Austin’s method to compute the sum of each series below.

1. $1+5+25+$$125+625+$$3125+15,625$

If the given series is $S$, compute $5S − S$.

Did you get $4S = 78{,}124 - 1$?

2. $5+15+$$45+...+885,735$

Identify the common ratio, $r$.
Then, if the given series is $S$, compute $rS − S$.