APK Install Issue

I bought a Nexus 7 for my son (so he would stop tying down my phone with playing games) everything has worked perfectly and all apks have installed fine but one...Hungry Shark Evolution. When I try to install from the Playstore I get the 505 error, when I try to install a downloaded apk I get "app not installed" my unknown sources box is checked and I have tried clearing cache. It is running stock Android 5.1.1, any help or pointers would be greatly appreciated. I am to the point of considering rooting, custom recovery, and flashing a rom if I have to. I just didn't feel like having to mess with his tablet on top of my and my wife's phone all the time (both our devices run custom roms). That is why I went with a Nexus so it got the new software in a timely manner.

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