Sync them back from iTunes on your computer - if you were syncing with iTunes in the first place. If you were not using iTunes - go to the purchased tab of the app store on your iPad and download them again. There will be no charge as long as you use the same Apple ID that you bought the apps with.
If you were using iCloud, you should have been able to restore from the iCloud backup in order to recover all of you apps, app data, device settings, etc.
How to backup and restore from a backup