Two things you can do. As mentioned above, go to play store, my apps and above each section is the total count of installed apps to be updated and total count of installed apps. You can also install app management programs (I have app monster) which give you a count of your apps.
For my situation, play store reports that I have installed 138 apps. App Monster reports 171 apps (which includes the 33 bloatware apps that Verizon thought I wanted on my phone).
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