Disclaimer: Exchange rates vary almost on a constant basis, so it is best to always have an up-to-date chart from an online source. For the purposes of this problem, we don't have to worry about the rates changing.
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25 U.S Dollars = 20 Euros
25/20 U.S. Dollars = 20/20 Euros
1.25 U.S. Dollars = 1 Euro
Saying "per Euro" is the same as saying "per 1 Euro". I divided both sides of the second equation by 20 so that I could turn the "20 Euros" into "1 Euro".
