diff --git a/MECHANICS_OF_SOLIDS_by_S.S._Bhavikatti/Chapter6.ipynb b/MECHANICS_OF_SOLIDS_by_S.S._Bhavikatti/Chapter6.ipynb
index 55339520..3935dbc3 100644
--- a/MECHANICS_OF_SOLIDS_by_S.S._Bhavikatti/Chapter6.ipynb
+++ b/MECHANICS_OF_SOLIDS_by_S.S._Bhavikatti/Chapter6.ipynb
@@ -1387,7 +1387,7 @@
     "W=40000.0              #effort\n",
     "R = 400  #Lever length\n",
     "u = 0.12    #coefficient of friction between screw and nut\n",
-    "P = (d/(2*R))*W*((u+(p/(3.14*D)))/(1-u*(p/(3.14*D))))   #Effort\n",
+    "P = (D/(2*R))*W*((u+(p/(3.14*D)))/(1-u*(p/(3.14*D))))   #Effort\n",
     "print \"Effort is\",P,\"N\"\n"
    ]
   },