Say a bank has 1 billion dollars deposited by individuals with bank accounts. How much of this does the banks lend/invest? Obviously it can't lend all of it or when I go to the bank there would be no money for me to take out. I realize this probably varies between institutions but in general about how much.
Also, what factors would contribute to the percentage they lend relative to the amount the bank has. For example, interest rates, inflation etc.