The gold standard system is essentially a fixed exchange rate regime. Instead of fixing the value of currencies to each other, countries fixed the value of their currencies to that of gold.

Suppose that in the U.K., the price of one ounce of gold is 5 and in the U.S., the price is $20. Let the U.K. be the domestic country. The nominal exchange rate between the pound sterling and the U.S. dollar is ________. (Note: Please type in decimal.)