I'm not sure how to solve this or even how to set up the equation.

Question

Melissa Patterson won $12000 in a contest. She decided to invest part of the money at 3% simple interest, and put the rest in an investment paying 4% simple interest. At the end of the year, she earned $440. How much did she invest at each rate?

Answer 1

a = part of Melissa's earnings

b = other part of Melissa's earnings

 

a+b = 12000

.03a + .04b = 440

 

Multiply the second equation by 25. You get

 

a+b = 12000

.75a + b = 11000

 

Subtract the second equation from the first one:

 

.25a = 1000

 

a = 4000

b = 8000