libapache2-mod-php5 versus apache2-mpm-worker

[thufir]

root at dur:/var/www# aptitude install  libapache2-mod-php5  
The following NEW packages will be installed:
  apache2-mpm-prefork{ab} libapache2-mod-php5 
0 packages upgraded, 2 newly installed, 0 to remove and 2 not upgraded.
Need to get 3,111 kB of archives. After unpacking 8,445 kB will be used.
The following packages have unmet dependencies:
 apache2-mpm-prefork : Conflicts: apache2-mpm which is a virtual package.
 apache2-mpm-worker : Conflicts: apache2-mpm which is a virtual package.
The following actions will resolve these dependencies:

     Remove the following packages:
1)     apache2-mpm-worker          





http://packages.ubuntu.com/precise/apache2-mpm-worker shows that this is 
for common files.

Did I install the php module incorrectly?




thanks,

Thufir