Martha's $18,750 is invested in two accounts, one earning 12% interest and the other earning 10%. After 1 year, her combined interest income is $2,117. How much has she invested at each rate?

Answer 1

let $ be the amount at 12 percent
$*0.12+ (18750-$)*0.10=2117
solve for $
$*.02=2117-1875
$=12,100 check that, so then the other is 18750-12,100=6,650

Answer 2

If x is invested at 12%, then the rest (18750-x) is at 10%
So, just add up the interest:

0.12x + 0.10(18750-x) = 2117