Click on Menu >> Accessories >> Terminal
sudo apt-get install numlockx
Type in your sudo password and press <ENTER>
Click on Menu >> Preferences > Default applications for LXSession.
Click on the Autostart tab.
Under Manual autostarted applications, type numlockx in the box and click Add.
|This is what LXSession configuration should look like, once you have made the change.|
You can reboot to test, but it should work. It works on my Lenovo, but there are people that report that it does not work on their machines.