diff --git a/chapter01.tex b/chapter01.tex
index 874f514..5428966 100644
--- a/chapter01.tex
+++ b/chapter01.tex
@@ -594,7 +594,7 @@ using the formula
 \[a + ak + ak^2 + \cdots + b = \frac{bk-a}{k-1}\]
 where $a$ is the first number,
 $b$ is the last number and the
-ratio between consecutive numbers is $x$.
+ratio between consecutive numbers is $k$.
 For example,
 \[3+6+12+24=\frac{24 \cdot 2 - 3}{2-1} = 45.\]