Doris invested some money at 7% and some money at 8%. She invested $6000 more at 8% than she did at 7%. Her total yearly interest from the two investments was $780. How much did Doris invest at each rate?

Answer 1

amount invested at 7% ---- x
amount invested at 8% = x+6000

solve for x:

.07x + .08(x+6000) = 780