Application of Four-Rate Formula and Exchange Rate Formula to demonstration of single currency with different value and interest rate

Putting the theory of price system on the relationship among price, wage, labor time, interest rate and GNP (or GDP), four main variables in economics, Four-Rate Formula and Exchange Rate Formula are created (Xiaozhong Zhai 2003). Two formulas applying to analyses of economy and calculation can show some valuable data to macroeconomics, economist and policymaker. They can produce a proof to demonstrate that single currency, for example, single European currency with different value and interest rate in different conditions and regions, can not certainly benefit price stability, sound public finances, low interest rates, incentives for growth, investment and employment. Two formulas are very simple, practical and easy to deal with the complex phenomenon in economy. Exchange Rate Formula has an immediate signification in the international trade economy.