reinstal operating system

[AC Question]

I was recently given an Andriod tablet & I have it reformatted , but it appears that the operating system is now gone. How can I get it back , please help

 

[B. Diddy]

Welcome to Android Central! What is the brand and model of the tablet? Did the previous owner root it, or did you? It's impossible to delete the OS unless the device is rooted.