Question

What is the sum of a 7-term geometric series if the first term is 6, the last term is 24,576, and the common ratio is -4?

Answer 1

`19,662`

Explanation:

There may be some nice formula for this (if so, someone please add it as a better answer).

To avoid too much thought I simply decided to evaluate the 7 terms and sum them (and because I'm feeling lazy, I let my spreadsheet to the actual calculations).

Note that there is redundant information in this question; we didn't need to be told both that there were `7` terms and that the final term value was `24,576`