exchange rate
Changing one measure for another is known as exchange – one measure replaces another measure.
We can think about this in the context of going on holiday to a foreign country.
Steffan is going on holiday to Spain. The country’s currency is the euro (€). The exchange rate is £1 = €1.14. This means for every pound Steffan exchanges, he will get €1.14.
Steffan wants to exchange £400.
Therefore, 400 × 1.14 = €456
This means that Steffan has €456 to spend on his holiday.