how to divide my value at run time in c#

Question

hi frnds...

 

 

i have two form first: in which only insert current dollar price... 65

 

and second: form in which  we insert product:

 

 

name:

size:

price: 500 rupees 

 

but when show this product in datalist control then 

 

price show in dollar at run time like 500/65=     7.69$

 

 

when we change dollar price like=60

 

then all price change according to this dollar price = all rupees/current dollar