title: how to change text in a TextView dynamically based on another TextView
body: <p>Good morning everyone. 
  I know from the title it's everything confused, so I will try to explain it better. 
  I need to create an app for a medical project to calc HbA1c. I have 3 editText in which I type values of medical test. Each of three changes because of other one. For example: if I have 42 in one, the other one is 5.99%. And so on. I'm trying to make them change dynamically: change still during I'm writing. 
  I tried using an OnCliclListener but I have to write the entire value. </p>
  
  <p>I don't know if I explain myself as good to make you understand. </p>
  
  <p>Thank you very much </p>