diff --git a/Lecture 6/Interval estimation.ipynb b/Lecture 6/Interval estimation.ipynb
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+{
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+   "source": [
+    "## Confidence intervals\n",
+    "\n",
+    "n=10\n",
+    "mu = 12\n",
+    "sigma = 2\n",
+    "alpha = 0.05\n",
+    "\n",
+    "data <- rnorm(n,mu,sigma)\n",
+    "\n",
+    "plot(data,rep(0,n),col=\"blue\")\n",
+    "abline(v=mu,col=\"red\")\n",
+    "abline(v=mean(data),col=\"blue\")\n",
+    "\n",
+    "lb=mean(data)-sigma/sqrt(n)*qnorm(1-alpha/2)  # This is the lower bound of the confidence interval\n",
+    "ub=mean(data)+sigma/sqrt(n)*qnorm(1-alpha/2)  # Upper bound.\n",
+    "\n",
+    "rect(lb,-0.5,ub,0.5)\n",
+    "\n",
+    "text(mean(data)-0.4,1,labels = \"mean\",col=\"blue\")\n",
+    "text(mu+0.3,-1,labels = \"mu\",col=\"red\")\n"
+   ]
+  }
+ ],
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