diff --git a/book/syntax_exercises/009.md b/book/syntax_exercises/009.md
index ce51f6f..077984c 100644
--- a/book/syntax_exercises/009.md
+++ b/book/syntax_exercises/009.md
@@ -31,7 +31,7 @@ $$ E = m \ccdot c^2 $$
 
 4. Check whether the equations renders correctly by clicking `preview`. Note that all ill-formatted equation are indicated in red, i.e. $\red{\text{\ccdot}}$
 
-5. As an alternative you try and use the 'math directive'. This will have the same results + adds a equation number which can be used for referencing:
+5. As an alternative you try and use the 'math directive'. This will have the same results + adds a equation number which can be used for referencing (refer to [Exercise 11](011.md)):
 
 ````md
 ```{math}