yum installs the package with the highest version number, regardless of the repository. You can change yum to install packages from a specific repository, even when another repository has a higher version number.
Warning
yum to not install security updates and accidentally leave your computer vulnerable to attack.
/etc/yum/pluginconf.d/priorities.conf exists, and contains the following text: enabled = 1. If you want to stop using the plugin, you can edit this file so it contains enabled = 0. This does not affect the priorities set in the repository configuration files.
/etc/yum.repos.d/* directory, adding a line like: priority = N where N is a number between 1 and 99, inclusive. A priority of 1 is the highest setting, and 99 is the lowest. You will need to set priorities of at least two repositories before this becomes useful.