There are 3 countries, A, B and C, whose currencies are $A, $B and $C respectively. Countries A and B have an agreement regarding trade in oil, so there is no barrier to trade in oil between them. Thus, the single price law applies in this case. Suppose the price of a barrel of oil in A is A$ 100 and in B it is B$ 20.

On the other hand, between B and C there are no costs for trading gold. In other words, the single price law applies in this case. The price of an ounce of gold in B is B$ 80 and in C is C$ 200.

What will be the nominal exchange rate between countries A and C?