diff --git a/Chapter15/example3.py b/Chapter15/example3.py
index d5b085b..77d1489 100644
--- a/Chapter15/example3.py
+++ b/Chapter15/example3.py
@@ -43,8 +43,10 @@ def countdown(n):
 
     pool = Pool(processes=2)
     start = time.time()
-    pool.apply_async(countdown, args=(COUNT//2,))
-    pool.apply_async(countdown, args=(COUNT//2,))
+    r1 = pool.apply_async(countdown, args=(COUNT//2,))
+    r2 = pool.apply_async(countdown, args=(COUNT//2,))
+    r1.wait() # it should wait to measure its completion time. 
+    r2.wait() 
     pool.close()
     pool.join()