You wrote it yourself in your last example ...

5507 x 20 = ~ 110 000
110 000 / 3 = 110 000 x 0.333 = 33 000+ 3300 + 330 = 36630... ( so much easier this way ...)

36630 - 550 = 36120

may be it was not clear enough from me: you take 10% of the Euros number off the result in Francs ...

error is always less than 1/1000 ...sufficient for a first comparison, no ???

Also note i'll never buy components for 5500 Euros !!!

Alain