putting the service-profit chain to work It eventually admitted that the app had broken down, but that it had been selling at 17 pounds at the station. However, when I got the reply, I had already paid the extra fee before the early discount ended. In this way, if the interest rate of a country is higher than that of other countries, it will attract a large amount of capital inflow, and the outflow of funds from the country will decrease, leading to the buying of this currency in the international market. At the same time, the capital account balance has been improved, and the currency exchange rate has been raised. On the other hand, if a country is loose credit, interest rates fell, if interest rates lower than in other countries, can cause large capital outflows, foreign capital inflows to reduce, the capital account balance of payments deteriorates, while selling the currency in foreign exchange market, caused the exchange rate to fall. Interest rate, in the form of expression, refers to the ratio of the amount of interest to the total amount of borrowed capital in a certain period of time.  the interest rate is the interest level per unit time of the unit currency, indicating the interest rate. Economists have been looking for a theory that can fully explain the structure and change of interest rates. Interest rates are usually controlled by the central bank of the country and administered by the federal reserve board in the United States. Today, interest rates are one of the important tools for macroeconomic regulation. According to Jerome McCarthy, "basic marketing" : a market is a group of potential customers with the same needs; They are willing to trade the goods or services offered by the seller in exchange for something of value, which is the way to meet the demand. Investment in securities is conducive to adjusting capital investment and improving the efficiency of capital use, thus guiding the rational flow of resources and realizing optimal allocation of resources.