60 / 50 = x / 70....60 U.S. to 50 euro = x U.S to 70 euro
cross multiply because this is a proportion
(50)(x) = (70)(60)
50x = 4200
x = 4200/50
x = 84 <== so 84 U.S dollars = 70 euros
proportions are nothing but equivalent fractions..
60/50 = 1.2
84/70 = 1.2
and as u can see, these are equivalent....so this is reasonable