[Q] There is insufficient space on the device topic

OK here's the deal i'm using a lollipop build (same problem with KK) and i'm not a math genius but i know that
714MB+200MB+94MB its not 2GB(1.97 TO BE EXACT). im trying to install an app and i get the following error
"error downloading "app name" there is insufficient space on the device"
i've tried clearing play store and services cache but without success :(
anyone have encountered this problem?

P.S. the app i've i'm trying to install is 6MB

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