How to calculate sum of series (Excel FV function?)

Factual Questions
1

In the game Cookie Clicker (don’t go there unless you want to be sucked into the universe’s biggest time waster) you buy buildings. Each building you buy will be 15% more expensive than the previous. I want to know if the current cost is X, how much will N buildings cost?

The game has a feature that will tell you how much 10 buildings will cost. In Excel I duplicated this result with X + 1.15X + 1.151.15X + 1.151.15*1.15X … etc

The game will tell you the cost of 1, 10, or 100. I want to know 50 or 17 or whatever.

I tried the Excel FV function and couldn’t get it to work. Any help would be greatly appreciated!

2

It’s a geometric series, looks like :

The sum is = X (1.15^n -1)/(1.15 -1) where n is the number of terms.

3

Or, for a quick rule of thumb, 50 of a building will cost approximately 1000 times as much as buying one, and buying 5 more will cost about as much as all of the buildings of that type you’ve already bought combined.

4

got it, thanks!

5

Hey if you want to try a version of this game that is

(1) got a fun and moderately thought provoking story
(2) solvable in a single session

Try paperclip maximizer: http://www.decisionproblem.com/paperclips/