This little-known Google app will pay you to do simple surveys on your smartphone

Google has grown into a huge global empire off the back of its free apps and services.

Rather than charging you to use things like Google Search or its mobile operating system Android, it provides them free of charge, then makes most of its money off the back of advertising revenues.

But one of Google's apps goes one step further - and actually pays you to use it.

Google Opinion Rewards is a little-known app that asks you simple surveys, and rewards you with free credit for the Google Play Store.

Here's how it works ...