Question

Susan invests twice as much money at 7.5% as she does at 6%. If her total interest after a year is $840 how much does she have invested at each rate?

Answer 1

Let x be the amount invested at 6%

840 = 0.06x + 0.075(2x)
840 = 0.06x + 0.15x
840 = 0.21x
x = 840/0.21
x = 4000

Therefore, she invests $4000 at 6% and $8000 at 7.5%