International Economics 10th Edition by Paul Krugman,Maurice Obstfeld ,Marc Melitz

Exercise 3

Table reports exchange rates not only against the US dollar, but also against the euro and the pound sterling. (Each row gives the price of the dollar, euro, and pound, respectively, in terms of a different currency.) At the same time, the table gives the spot dollar prices of the euro ($1.3221 per euro) and the pound sterling ($1.5539 per pound). Pick any five currencies from the table and show that the three quoted spot exchange rates (in terms of dollars, euros, and pounds) approximately rule out triangular arbitrage. Why do we need to add the word "approximately"?
Exchange Rate Quotations