14.04 - sudo apt-get install npm error

When I was about to install nodejs I successfully ran these two commands:

sudo apt-get update

sudo apt-get install nodejs

However, when I ran sudo-apt-get install npm it gave me this list of errors:

$ sudo apt-get install npm
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have

requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 npm : Depends: nodejs but it is not going to be installed
       Depends: node-abbrev (>= 1.0.4) but it is not going to be installed
       Depends: node-ansi but it is not going to be installed
       Depends: node-archy but it is not going to be installed

       Depends: node-block-stream but it is not going to be installed
       Depends: node-fstream (>= 0.1.22) but it is not going to be installed
       Depends: node-fstream-ignore but it is not going to be installed
       Depends: node-github-url-from-git but it is not going to be installed
       Depends: node-glob (>= 3.1.21) but it is not going to be installed
       Depends: node-graceful-fs (>= 2.0.0) but it is not going to be installed
       Depends: node-inherits but it is not going to be installed
       Depends: node-ini (>= 1.1.0) but it is not going to be installed
       Depends: node-lockfile but it is not going to be installed
       Depends: node-lru-cache (>= 2.3.0) but it is not going to be installed

       Depends: node-minimatch (>= 0.2.11) but it is not going to be installed
       Depends: node-mkdirp (>= 0.3.3) but it is not going to be installed
       Depends: node-gyp (>= 0.10.9) but it is not going to be installed
       Depends: node-nopt (>= 2.1.1) but it is not going to be installed
       Depends: node-npmlog but it is not going to be installed
       Depends: node-once but it is not going to be installed
       Depends: node-osenv but it is not going to be installed
       Depends: node-read but it is not going to be installed
       Depends: node-read-package-json (>= 1.1.0) but it is not going to be installed
       Depends: node-request (>= 2.25.0) but it is not going to be installed

       Depends: node-retry but it is not going to be installed
       Depends: node-rimraf (>= 2.2.2) but it is not going to be installed
       Depends: node-semver (>= 2.1.0) but it is not going to be installed
       Depends: node-sha but it is not going to be installed
       Depends: node-slide but it is not going to be installed
       Depends: node-tar (>= 0.1.18) but it is not going to be installed
       Depends: node-which but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

I tried these:
http://www.scriptscoop.net/t/853c92c3dcf6/node-js-cannot-be-installed-in-ubuntu.html

https://www.digitalocean.com/community/tutorials/how-to-install-node-js-on-an-ubuntu-14-04-server

EDIT:

this is not a proper way to install Node.js anyway, instead NVM (Node version manager) should be used. See here: https://github.com/creationix/nvm

check with following code :

sudo apt-get install python-software-properties python g++ make
sudo add-apt-repository ppa:chris-lea/node.js
sudo apt-get update
sudo apt-get install nodejs
npm install

to check version,

npm -v 

output will be like this

1.4.28