a woman has $27,000. Part is invested at 7% interest and the rest is invested at 9% interest. If the total interest earned is $2110, how much does she invest at each rate?

Answer 1

.07 x + .09 (27000 - x) = 2110
- .02 x = 2100 - 2430 = - 330
x = 16,500
27000 - x = 10,500

Answer 2

part at 7% --- x
part at 9% ---- 27000-x

.07x + .09(27000-x) = 2110
times 100
7x + 9(27000-x) = 211000

solve for x

(why not invest all at 9% ? )