diff --git a/extras/courses.md b/extras/courses.md
index 273ea3b..1d0f356 100644
--- a/extras/courses.md
+++ b/extras/courses.md
@@ -22,8 +22,6 @@ Courses | Duration | Effort
 
 Courses | Duration | Effort
 :-- | :--: | :--:
-[Pre-Calculus](https://www.coursera.org/course/precalculus)| 10 weeks | 10-12 hours/week
-[Multivariable Calculus](https://www.coursera.org/course/m2o2c2)| 6 weeks | 5-7 hours/week
 [Introduction to Probability and Data](https://www.coursera.org/learn/probability-intro)| - | -
 
 ## Systems
@@ -31,15 +29,8 @@ Courses | Duration | Effort
 Courses | Duration | Effort
 :-- | :--: | :--:
 [Operating System Engineering](http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-828-operating-system-engineering-fall-2012/) | - | -
-[Introduction to Linux](https://www.edx.org/course/introduction-linux-linuxfoundationx-lfs101x-0)| 8 weeks | 5-8 hours/week
-[CompTIA Linux+](https://www.cybrary.it/course/comptia-linux-plus/)| - | 5.25 hours
 [Introduction to Operating Systems](https://www.udacity.com/course/introduction-to-operating-systems--ud923)| 8 weeks | 5-8 hours/week
 [Advanced Operating Systems](https://www.udacity.com/course/advanced-operating-systems--ud189)| 5 weeks | 5-8 hours/week
-[Advanced Operating Systems: Structures And Implementation](https://www.youtube.com/playlist?list=PL-XXv-cvA_iB_5Q8G8kW5idSwNmXypmQE)| 10 weeks | 2-3 hours/week
-[Introduction to Computer Networking](https://lagunita.stanford.edu/courses/Engineering/Networking-SP/SelfPaced/about) | - | 5-10 hours/week
-[CompTIA Network+](https://www.cybrary.it/course/comptia-network-plus/) | - | 32 hours
-[Cisco CCNA](https://www.cybrary.it/course/cisco-ccna/) | - | 15.5 hours
-[Networking for Web Developers](https://www.udacity.com/course/networking-for-web-developers--ud256) | - | 12 hours
 [Computer Networking](https://www.udacity.com/course/computer-networking--ud436) | 12 weeks | 5-8 hours/week
 
 ## Theory