Ok so I have a Tesla TTL7 tablet with android version 4.4 and the thing is my current apps take like 1.37 GB and I have 5 GB of space remaining but I still cannot download apps. And as I mentioned in the title it says that my internal and sd memory are the same thing(sd adds space to internal).
Storage on SD-card and internal storage are quite different.
You can save files directly on the device's internal storage. By default, files saved to the internal storage are private to your application and other applications cannot access them (nor can the user). When the user uninstalls your application, these files are removed.
Every Android-compatible device supports a shared "external storage" that you can use to save files. This can be a removable storage media (such as an SD card) or an internal (non-removable) storage. Files saved to the external storage are world-readable and can be modified by the user when they enable USB mass storage to transfer files on a computer.
Caution: External storage can become unavailable if the user mounts the external storage on a computer or removes the media, and there's no security enforced upon files you save to the external storage. All applications can read and write files placed on the external storage and the user can remove them.
This explanaton is given on the Android-Developer-Site