Q: erase ipad when I do not know my Restrictions Passcode?

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Forgotten Restrictions Passcode Help

You will need to restore your device as New to remove a Restrictions passcode. Go through the normal process to restore your device, but when you see the options to restore as New or from a backup, be sure to choose New.

Also, see iTunes- Restoring iOS software.

Follow the instructions in  iOS: How to back up your data and set up your device as a new device http://support.apple.com/kb/HT4137 to restore the device to factory settings.

Once you have setup the device as a new one, you can then sync it back with your iTunes account and all your music, apps, contacts and any other content sync'ed with iTunes will be loaded on the device. Any content that is stored only on the device and not sync'ed with iTunes, like app logins or data, will be lost during this process. Be forewarned that this is a long process and can take a couple of hours or more to complete. This can be painful, but it is necessarily so to prevent users from working around the security settings. After the restore is complete, you can setup a new Restrictions passcode. Make a note of the passcode to avoid this situation in future.

 Cheers, Tom