Q. What do you mean by Exchange rate?
Exchange rate is defined as the price of one unit of currency in terms of another currency. If one euro costs 1.5 USD then 1 USD costs 1/1.5 = 0.667 euro. If exchange rate is stated in terms of euro (for instance 1.5 USD/euro) then euro is known as the base currency or unit currency.
In most countries, exchange rate is expressed using foreign currency as the base currency. For instance in Denmark, USD exchange rate would be expressed as 4.8 Danish kronor (DKK) per USD whereas, in the U.S., same exchange rate would be expressed as 0.208 USD/DKK (or 20.8 USD/100DKK). This way of specifying the exchange rate is known as the direct method as you can immediately figure out how much you have to pay for one unit of a foreign currency.
In a number of countries, exchange rate is expressed using home currency as the base currency. In the UK for instance, Danish exchange rate would be expressed as 9.2 DKK/GBP. So you have to invert the exchange rate if you want to figure out how much one unit of a foreign currency costs in the UK. This method is known as the indirect method of specifying the exchange rate and notation is occasionallytermed as British notation.