# Finite geometric series word problems

Understanding and solving problems with the formula for a finite geometric series.

### Problem

Seo-Yeon takes a dose of 400 international units left parenthesis, I, U, right parenthesis of a certain supplement each day. Approximately start fraction, 1, divided by, 3, end fraction of the supplement remains in the body after each day.
How much of the supplement is in Seo-Yeon's body immediately after the 21, start superscript, s, t, end superscript dose?