diff --git a/exam/ex.tex b/exam/ex.tex
index c5275f6..b42e681 100644
--- a/exam/ex.tex
+++ b/exam/ex.tex
@@ -181,7 +181,9 @@
       $\unit[655]{bit}$ input to map to 101 zeros. Therefore, the whole search
       space is $2^{101}$ and the probability with one query is $1/2^{101}$.
 
-    \item \TODO
+    \item If the adversary makes one inverse query, the probability that it hits
+      a preimage is $1/2^{55+90} = 1/2^{145}$. This is due to the fact that the
+      first $\unit[55]{bits}$ and the last $\unit[90]{bits}$ have to be zeros.
 
     \item \TODO