Chapter 1 - Section 1.7 - Modeling with Equations - 1.7 Exercises - Page 75: 28

6%

He invested two amounts at two different interest rates that we do not know. 1000 dollars at x interest rate and 2000 dollars at x+0.005 (half percent higher interest rate), we know that he will receive 190 total interest. 1000x +2000(x+0.005)=190 1000x 2000x+10=190 3000x=180 x=0.06=6%