diff --git a/labs/11_hash_tables/README.md b/labs/11_hash_tables/README.md
index 25d9f1a..f9bcf5b 100644
--- a/labs/11_hash_tables/README.md
+++ b/labs/11_hash_tables/README.md
@@ -85,3 +85,5 @@ Explanation: The longest consecutive elements sequence is [0, 1, 2, 3, 4, 5, 6,
 ```
 
 **To complete this checkpoint**: Show a TA your program and the test results.
+
+**Note**, checkpoint 3 is very challenging, if you can't get it work during your lab period, make sure you understand it completely after the lab period, because one of the four problems on Test 3, will be about separate-chaining-based hash tables. It's 100% certain.