You can multiply apples and oranges. It all depends on the situation.
Let us suppose that in a country apples are very scarce and oranges are
abundent. Suppose two farmers want to barter apples and oranges.If
the exchange rate is 5 oranges for an apple, the farmer who wants
10 apples has to give
10 apples X 5 oranges = 50 oranges !
Whenever we want purchase an American book in India we have to
multiply the cost of the book in dollars with exchange rate in rupees
to get an answer in rupees.
regards,