The available balance also needs to be calculated based on the first step + the compensation balance × the statutory deposit reserve ratio

So it is estimated that the net amount of loanable funds = 400-(400×20 %+100×5%)+(400×20%+100×5%)×10%=323.5

That is, the pre-tax rate of return is 81÷323.5=25.04%

Moreover, from the bank's perspective, the calculation of interest expense/available loan amount is not accurate enough (this is from the customer's perspective), although the calculation process is the same.

The formula for this question is estimated bank pre-tax rate of return = estimated total loan income/estimated net loanable funds

Among them, estimated total loan income = loan income + commitment Fee income

Estimated net amount of loanable funds = net amount of loanable funds - compensation balance + compensation balance × statutory deposit reserve ratio