But if we want to evaluate the expressions anyways, we have 5(-2 + 4) - 3(-2 + 6) = 5 ⋅ 2 - 3 ⋅ 3 = 10 - 12 = -2 on the left, and 9(-2 + 1) = 9 ⋅-1 = -9. Because - 2\mathrel{≠} - 9, -2 is not a solution.
Percent | Investment | Interest |
0.03 | x | 0.03 ⋅ x |
0.04 | 12\kern 1.66702pt 000 - x | 0.04 ⋅ (12\kern 1.66702pt 000 - x) |
12 000 | 440 |
So 0.03 ⋅ x + 0.04 ⋅ (12\kern 1.66702pt 000 - x) = 440. Solving for x, \mathbf{x = 4000}.
He invested $4 000 at 3% interest and $8 000 at 4% interest. Checking, this totals to 0.03 ⋅ 4000 + 0.04 ⋅ 8000 = 120 + 320 = 440.