I have a main Activity which contains two Fragments (Each in it's own activity) as ActionTabListener

Everytime I hit the Calculate button I want the information to append on top of what's already under Display Result activity textbox and not overwrite. I tried SharedPreference, but it only works to setText() but .append() doesn't work.
The TextBox is initialized under the Display Trip as
private EditText showLog;
Should I change it to private?
How do I transfer information between the two activities without losing them within the duration of the application in the memory?