Every time I install an app in app store on iPad, the app store will close. This is annoying when I want to install multiple apps at once. Is there a way to stop it from doing this?
Apple implemented this in iOS 6. Install iOS 6 and enjoy the updated appstore.
Without a jailbreak, no.
If you are willing to jailbreak your iPad, it appears this might solve your problem.
You will need to jailbreak your device and install the tweak called StayOpened by searching for it in Cydia. If you need assistance with the jail breaking process, check out http://jailbreakqa.com/
In fact, there is yet another tweak (in Cydia) that optimizes the iOS installation process by automatically entering your password for you. It's called PasswordPilot. Note: It would be wise to lock your phone with a passcode afterwards for security.