ormat Tools Extensions Help Last edit was seconds ago Normal text Times New.. - 12 + BIU A . 15 3 6 01 4. Johnny invested $20,000. A portion returned 5% and another portion returned 8%. The total interest earned on the investment was $1150. Write a system of equations for this situation and determine how much of the original investment was invested at the 5% rate and how much was invested at the 8% rate. Answer: Let x be the amount invested that earned 5% and y be the amount invested that earned 8%. System of equations: 1's equation: 2nd equation: Solution: X = $. Solve the system by writing a matrix equation, then solve using the inverse with a calculator. Make sure and enter your matrix equation in space provided below 5. You have 37 coins that are nickels, dimes, and pennies. The total value of the coins is $1.55. There are twice as many pennies as dimes. Find the number of each type of coin in the bank. Answer: Let n be the number of nickels, d be the number of dimes, and p be the number of pennies. The system is 1" equation: 2"d equation: 3" equation: Matrix Equation