Ubuntu: How to fix 'W: Duplicate sources.list entry'?

The Question: I keep getting this warning whenever I try to run sudo apt-get update.
updates/main i386 Packages (/var/lib/apt/lists/
W: You may want to run apt-get update to correct these problems

How do I fix it?

Solutions Sample (Please watch the whole video to see all solutions, in order of how many people found them helpful):

== This solution helped 6 people ==
**** 10.10 and Earlier ****
Applications ＞ Ubuntu Software Center ＞ Edit ＞ Software Sources ＞ Other
Software
OR
System ＞ Administration ＞ Synaptic Packet Manager ＞ Settings ＞ Repositories
[Software Sources config window]
Select and Remove duplicate entries.

== This solution helped 2 people ==
Install ubuntu-tweak and remove the duplicate entries from there.
sudo add-apt-repository ppa:tualatrix/ppa
sudo apt-get update
sudo apt-get install ubuntu-tweak
[alt text]