well.. it depends on the info you have...
for example if you have:
1 Canadian= 0.8 US
and you want to convert 10 USD to canadain:
10 USD x 1 Canadian/ 0.8 US
if by some freak of nature the canadian dollar is worht more than the USD:
eg: 1US = 0.8 Can
then 10 US is
10 US x 0.8 Can/1US
so, as you can see, it depends on what conversion rate you have and what you want.
you can also set it up to always multiply or always divide, but you have to get the exchange rate in the correct terms.. to do that all you might have to do is take the inverse of the exchange rate. its up to you!
good luck!