The cheapest Big Mac in the world can be bought in China, while the Swiss have to pay nearly four times as much for the same burger. The Economist magazine's annual Big Mac Index found that McDonald's charged $1.20 for its burger in China and $4.52 in Switzerland. The Index said these statistics showed that the Chinese yuan was the most undervalued currency in the world, while the Swiss franc was the most overvalued. The Big Mac Index, introduced in 1986, compares burger prices in countries around the world, using the index as a rough guide to currency valuations. Euro...