Answer:
$10,000
Step-by-step explanation:
You can define a variable that represents the answer to the question: the amount invested at 3.5%. Let's say that is x. Then the amount invested at 5% is 16000-x, and the total interest earned is ...
0.035·x + 0.05·(16000 -x) = 650
-0.015x +800 = 650 . . . . . . . . . . . . simplify
-0.015x = -150 . . . . . . . . . . . . . . . . . subtract 800
x = 10,000 . . . . . . . . . . . . . . . . . . . . divide by -0.015
The amount that should be invested at 3.5% is $10,000.
