Go to iTunes on your computer, Devices, (your iPad), Apps (be patient – it takes a while for the apps from your iPad to come up), you’ll see a place to check Automatically sync new apps (after the listing of your apps).This should handle what is needed with every sync in the future.
If that didn’t solve the problem or it was already checked, try this: Connect your iPad to your computer. In iTunes on your computer, do File, Transfer Purchases from (name of your iPad).
