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A peek inside our wallets by the Federal Reserve Bank of San Francisco.

They did a study on how we spend money. Not on what do we spend money, but literally how does it get spent: Cash? Credit?

Here's how it breaks down:

By absolute number of transactions: Cash is king at 40 percent.

But once you take the value of transactions into account, it's a whole different ballgame.

The average value of a cash transaction is only $21, compared with $168 for checks and $44 bucks for debit cards.

Follow Kai Ryssdal at @kairyssdal