diff --git a/exam/ex.tex b/exam/ex.tex
index 393130f..c5275f6 100644
--- a/exam/ex.tex
+++ b/exam/ex.tex
@@ -176,7 +176,10 @@
       a valid preimage: $[F^P(x)=y]$ where $x$ and $y$ satisfy the
       aforementioned conditions.
 
-    \item \TODO
+    \item If the adversary makes one forward query, the probability that it hits
+      the target image is $1/2^{g} = 1/2^{101}$. The adversary wants to find a
+      $\unit[655]{bit}$ 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