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Ubuntu apt-get 'package has no installation candidate' error

I was trying to install a package using apt-get and realized that apt-get wouldn't install that or any other package. I found various suggestions to fix this problem:

Problem

$ sudo apt-get install scons
Reading package lists... Done
Building dependency tree      
Reading state information... Done
Package scons is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'scons' has no installation candidate

Solution:

$ sudo apt-get update

$ sudo apt-get install build-essential

$ sudo dpkg --configure -a

$ sudo apt-get -f install

None of those worked in my case. I then went to Ubuntu Software Center>Edit> Software Sources and made these changes.

After that the following commands did the job

$ sudo apt-get update

$ sudo apt-get install build-essential

$ sudo apt-get install scons