Final answer:
A bank can lend out 85% of its deposits if the required reserve ratio is 15%, as the reserve ratio determines what portion of the deposits must be kept in reserve, with the rest available for loans.
Step-by-step explanation:
The amount that a bank can lend out if the required reserve ratio is 0.15, or 15%, is 85% of its deposits. This is because the reserve ratio refers to the portion of depositors' balances that banks must have on hand as cash in their vaults or as deposits with the central bank. The remainder, which in this case is 85%, can be used for loans or other investments. This is known as the excess reserve and represents the amount by which actual reserves exceed the required reserves. Banks are essentially required to keep a fraction (the reserve ratio) of their deposits in reserve, but they are free to lend out the rest.