Exchange rate quotes, cross rates and % changes: CFA Level I
An exchange rate gives the price of one unit of the base currency in units of the quote currency. A cross rate between two currencies can be built from each one's rate against the US dollar so the dollar cancels. When a rate moves, the base currency's percentage change and the quote currency's are not equal and opposite, because each is measured from a different starting value.
Base and quote
The St. Louis Fed explains that an exchange rate is the value of one currency in terms of another. The base currency is the one being priced and the quote currency prices it. A rate of 0.88 Swiss francs per dollar means 1 USD = 0.88 CHF. The inverse, 1 / 0.88 = 1.14 dollars per franc, is an equally valid rate.
If the rate falls from 0.88 to 0.75 francs per dollar, the dollar buys fewer francs, so the dollar has weakened and the franc has strengthened. Each franc now costs 1 / 0.75 = 1.33 dollars, up from 1.14.
Conventions differ by currency. The Federal Reserve's H.10 release quotes most currencies in units per US dollar, such as yen or Canadian dollars per dollar, but quotes the euro, pound, Australian dollar and New Zealand dollar in US dollars per unit. Check which currency is the base before you calculate.
Cross rates
To get a rate between two non-dollar currencies, arrange the two dollar quotes so the dollar cancels.
Example 1: USD 1.10 per euro and JPY 150 per dollar. JPY per EUR = (USD per EUR) x (JPY per USD) = 1.10 x 150 = 165 yen per euro.
Example 2: USD 1.08 per euro and USD 0.73 per Canadian dollar. Both are in dollars per unit, so divide: CAD per EUR = 1.08 / 0.73 = 1.4795. Check the units: (USD/EUR) / (USD/CAD) = CAD/EUR.
Percentage changes
The base currency's change is the change in the rate: new rate / old rate - 1. The quote currency's change uses the inverse rates: old rate / new rate - 1.
Example: francs per dollar move from 0.90 to 0.80. The dollar's change is 0.80 / 0.90 - 1 = -11.1%. The franc's change is 0.90 / 0.80 - 1 = +12.5%. Check with inverses: 1 / 0.90 = 1.1111 and 1 / 0.80 = 1.25 dollars per franc, and 1.25 / 1.1111 - 1 = 12.5%.
Likewise, if the euro falls 4.00% against the yen, the yen rises 1 / 0.96 - 1 = 4.17% against the euro, not 4.00%.
Where the exam catches people
Believing a rising rate always means the domestic currency strengthened: a rise means the base currency strengthened, whichever currency that is.
Believing one currency's % depreciation equals the other's % appreciation: a 4% fall in one is a 4.17% rise in the other.
Believing a cross rate is found by multiplying any two quotes: arrange them so the common currency cancels, which sometimes means dividing.
Believing every currency is quoted per US dollar: the euro, pound, Australian dollar and New Zealand dollar are usually quoted in dollars per unit.