Doris invested some money at 7% and some money at 8%. She invested $5,000 more at 8% than she did at 7%. Her total yearly interest from the two investments was $850. How much did Doris invest at each rate?
A) $4,000 at 7%, $8,000 at 8%
B) $3,000 at 7%, $9,000 at 8%
C) $3,000 at 7%, $8,000 at 8%

Question

Quizplus · Accepted Answer

Let x be the amount invested at 7%. Then the amount invested at 8% is x+5000. The yearly interest from the 7% investment is 0.07x, and the yearly interest from the 8% investment is 0.08(x+5000). The total yearly interest is $850, so we have the equation:
0.07x + 0.08(x+5000) = 850
Simplifying and solving for x, we get:
0.07x + 0.08x + 400 = 850
0.15x = 450
x = 3000
Therefore, Doris invested $3000 at 7% and $8000 at 8%. The answer is choice C.

Doris Invested Some Money at 7% and Some Money at 8