Where the apps from google play get downloaded?
In older Android OS versions the apk files downloaded by Google Play Store were usually stored in either /cache/download or /data/local directories.

Now the temporary location is determined by the Download Provider service, and is usually found in /data/data/com.android.providers.downloads/cache directory.  Again, this may be different for various Android OS versions.  It can also vary if manufacturers modified the OS (e.g. Samsung's TouchWiz or HTC's Sense.)