There's been some chatter in the market this week about whether a bank may be in trouble. The source of the concern is an anomaly in the federal-funds rate, that's the rate banks charge each other to borrow money overnight.

Banks, however, have some discretion based on the borrowing bank's collateral and the supply and demand in the marketplace. So, it's not unusual to see the actual rate on overnight loans vary slightly. For instance, on June 23, the rate was between 0.1% and 0.375%. On June 24 it was between 0.1% and 0.5%.

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