Install R on Ubuntu 14.04

Update your local repository

sudo apt-get update

sudo vi /etc/apt/sources.list

Check http://cran.r-project.org/mirrors.html for the list of CRAN mirrors.

In the end of the file paste the below content

deb http://cran.rstudio.com/bin/linux/ubuntu trusty/

If your mirror is different from http://cran.rstudio.com then use
deb <mirror>/bin/linux/ubuntu trusty/
save and close

Update your local repositories with added libraries

sudo apt-get update*

Install R base and dev libraries

sudo apt-get install r-base-dev r-base