"How long do you earn enough money to buy a McDonald's 'Big Mac'?" If asked suddenly, most people may take a nap, because many people are usually more accustomed to another algorithm, that is, I The monthly salary is enough to buy a few "Big Macs"? These two questions seem to be the same thing, but there are obvious differences in statistical significance. The former looks at the value of labor as a commodity, but the latter? ['Use labor to examine the value of goods.', 'Use the value of goods to examine labor.', 'Use income to measure purchasing power.', 'Measure income with purchasing power.']