diff --git a/src/7_tight_binding_model_sol.md b/src/7_tight_binding_model_sol.md
index f61f521eabc1759050e1def0fad59dfd110b2555..6d1a683c70b8a643b0017a9a038253f3ad89fc82 100644
--- a/src/7_tight_binding_model_sol.md
+++ b/src/7_tight_binding_model_sol.md
@@ -52,5 +52,5 @@ pyplot.yticks([0.5, 1], [0, r'$\frac{L}{2\pi a}\sqrt{\frac{\kappa}{m}}$'])
 
 4.
 
-
+Hint: The group velocity is inversely proportional