Fed allows key interest rate to drop. (Federal Reserve Board)(National Business News)

The U.S. central bank, the Federal Reserve Board, allowed a key interest rate to slip on Wednesday last week, in a move analysts generally viewed as an additional effort to prod the nation's weak economy. The Fed does not announce changes in its target range for the federal funds rate, which is the rate banks charge each other for overnight loans, and some analysts said it would take a few days to be certain of the central bank's intentions. The Fed influences the funds rate level by adding or draining reserves from the banking system. Last week, when the funds rate fell to 5%, from 5.25%, the Fed failed to drain money from the system, as it normally would have done if it …