diff --git a/books.md b/books.md
index 15bf2dc..8283326 100644
--- a/books.md
+++ b/books.md
@@ -68,7 +68,7 @@ The following is a list of free, open source books on machine learning, statisti
 * [Introduction to statistical thought](http://people.math.umass.edu/~lavine/Book/book.pdf)
 * [Basic Probability Theory](http://www.math.uiuc.edu/~r-ash/BPT/BPT.pdf)
 * [Introduction to probability](https://math.dartmouth.edu/~prob/prob/prob.pdf) - By Dartmouth College
-* [Principle of Uncertainty](http://uncertainty.stat.cmu.edu/wp-content/uploads/2011/05/principles-of-uncertainty.pdf)
+* [Principle of Uncertainty](http://www.stat.cmu.edu/~kadane/principles.pdf)
 * [Probability & Statistics Cookbook](http://statistics.zone/)
 * [Advanced Data Analysis From An Elementary Point of View](http://www.stat.cmu.edu/~cshalizi/ADAfaEPoV/ADAfaEPoV.pdf) - Book
 * [Introduction to Probability](http://athenasc.com/probbook.html) -  Book and course by MIT
@@ -85,5 +85,5 @@ The following is a list of free, open source books on machine learning, statisti
 * [Linear Algebra Done Wrong](http://www.math.brown.edu/~treil/papers/LADW/LADW.html)
 * [Linear Algebra, Theory, and Applications](https://math.byu.edu/~klkuttle/Linearalgebra.pdf)
 * [Convex Optimization](http://web.stanford.edu/~boyd/cvxbook/bv_cvxbook.pdf)
-* [Applied Numerical Computing](http://www.seas.ucla.edu/~vandenbe/103/reader.pdf)
+* [Applied Numerical Computing](http://www.seas.ucla.edu/~vandenbe/ee133a.html)
 * [Applied Numerical Linear Algebra](http://egrcc.github.io/docs/math/applied-numerical-linear-algebra.pdf)