diff --git a/maximumsAndMinimums/exercises/maxMinSecondDerivativeTest4.tex b/maximumsAndMinimums/exercises/maxMinSecondDerivativeTest4.tex
index 39241711f..16018f0ab 100644
--- a/maximumsAndMinimums/exercises/maxMinSecondDerivativeTest4.tex
+++ b/maximumsAndMinimums/exercises/maxMinSecondDerivativeTest4.tex
@@ -16,14 +16,17 @@
 
 \begin{exercise}
 
-The function $f(x) = x\sqrt{4-x}$ has only one critical point, $x=a$.
+The function $f(x) = x\sqrt{4-x}$ has two critical points $a, b$ in ascending order,
 
 $$
-a = \answer{8/3}
+a = \answer{8/3} \textrm{ and } b = \answer{4}
 $$
 
 
-$f''(a)$ is \wordChoice{\choice{positive} \choice[correct]{negative}}, so $x=a$ is a local \wordChoice{\choice[correct]{max} \choice{min}}.
+$f''(a)$ is \wordChoice{\choice{positive} \choice[correct]{negative}}, so $x=a$ is a local \wordChoice{\choice[correct]{max} \choice{min}}. 
+\begin{hint}
+Note that we cannot apply the second derivative test on $x =b$, since $f''(b)$ does not exist. 
+\end{hint}
 
 \end{exercise}
 \end{document}