That's exactly what I said, not what he said. You keep 10% and loan 90%. He said they deposit $100 and then the bank loans out $900 (9x the deposit).
"Reserve requirements affect the potential of the banking system to create transaction deposits. If the reserve requirement is 10%, for example, a bank that receives a $100 deposit may lend out $90 of that deposit. If the borrower then writes a check to someone who deposits the $90, the bank receiving that deposit can lend out $81. As the process continues, the banking system can expand the change in excess reserves of $90 into a maximum of $1,000 of money ($100+$90+81+$72.90+...=$1,000), e.g.$100/0.10=$1,000."