1. Starting with the simplest cases, we find several virtual 1-to-1 ratios:

One U.S. Dollar = 1.00 Canadian Dollars = 0.96 Swiss Francs = 1.06 Australian Dollars.

2. Other roughly decimal links include Mexico, Japan, and South Korea:

One U.S. Dollar = 10.5 Pesos = 104 Yen = 1,043 Won.

3. Then, of course, there are two other E-Z ratios, the Pound and the Euro:

One Pound (£) = $1.96.

One Euro (€) = $1.55.

With a little poetic license (and a maximum rounding error of six percent, for the Australian Dollar), we can simplify these rates to make them easier to remember. In particular, the rounded numbers in the first table simplify the standard exercise of flipping (taking the reciprocal of) the exchange rates, to reverse the perspective.



The first column shows that one U.S. (or Canadian or Australian) Dollar equals about one Swiss Franc, 10 Pesos, 100 Yen, or 1,000 South Korean Won. The first row shows that one Peso equals about 10 cents (listed as .1 of one Dollar), one Yen equals one cent, and one Won equals 0.1 cent.

That feels E-Z, doesn’t it? But what about the Pound and the Euro? The Pound can be rounded from $1.96 to $2, and the Euro from $1.55 to $1.50 to keep the fractions simple. (The maximum rounding error here is less than four percent.) Then we’ll call $1.50 “³/₂ of a Dollar.”



Now the first column shows that a U.S. Dollar (or Canadian Dollar, or Australian Dollar, or a Swiss Franc) will buy ²/₃ of a Euro. The first row shows that a Euro will buy the reciprocal, ³/₂ of a Dollar. Similarly for the Euro and the Pound: ³/₄ and ⁴/₃.

Of course, most currencies are messier, including in particular the Chinese Yuan. It has risen nearly 20 percent recently but is still viewed by most observers as seriously undervalued. The Yuan now trades at about 14 cents, or about 7 to the U.S. dollar. But who knows? Maybe a year from now it will have risen enough (or the Dollar will have fallen enough) to make the numbers easier to remember.