how can I changed data in textbox 2 when put data in textbox1(textbox using gridview) in gridview

I want when put data in textbox2 the data in text box1 is changed (textbox using gridview) in gridview
what the control for do it
and in any event  I can do it
when put number 50 in textbox2 show the result in textbox1 50*100
without click any button
please help me