1. 'Let's do the math' applications do not collect any personally identifiable information.
2. The only information which is sent to the central repository (hosted on Amazon) is information about number of tasks solved by user of application. This information is published in anonymous way. So any personal information can not be retrieved from. Token used to identify application is generate randomly without any personal data.
3. Sending information to central repository is configured in option Settings. By default it is disabled.