Using the same Apple iTunes account on all your iOS devices allows you to Sync purchases across them. This can save you some serious time and cash. Here’s how you can control the syncing of purchased apps across your iPad, iPod and iPhone.
Tap Settings >> Store.
In the Store settings, adjust which apps should Automatically Download purchases from your iTunes account.
The Store settings are individual to each iOS device so you will need to repeat this process on each of your iOS devices.