IntelliJ Idea two APK files

Question

I am using IntelliJ Idea for Android development. I want to release the app for beta testing but after building the app there are two apk's one inside app folder and another inside the app folder/bin directory both have different sizes, one inside the bin folder in bigger than the one inside the app folder.

My Question

1. Why there are two apks?
2. Why both the apk's have different sizes?
3. Which one should be used for beta distribution by email?

Answer 1

The suggestion of @cracycoder worked

"Check Android facet settings and the module settings for the output directories configuration. – CrazyCoder Oct 28 at 21:54"