Final answer:
The optimal interest rates would reflect the expected rate of return and associated risk of each type of borrower, ensuring a higher return than what the FED provides and suitable compensation for default risk.
Step-by-step explanation:
The question revolves around the idea of lending by commercial banks to two different types of borrowers in a competitive market, and the interest rates that should be charged to each if the banks could differentiate between the two types. Given the default risk of the borrowers and the certainty of a return from the Federal Reserve (FED), a bank would prefer to charge an interest rate that reflects the expected rate of return and the risk associated with each type of borrower.
The high type borrower has an expected return of 1.6 (0.8*2) with a lower risk, while the low type borrower has an expected return of 0.5 (0.1*5) with a higher risk. If the bank could distinguish between them, charging a rate that ensures a return higher than what the Federal Reserve offers (which is 1) while compensating for the risk involved would be the optimal strategy.