
You are going to invest $25, 000, part at 14% and part at 16%. What is the most that can be invested at 14% in order to make at least $3,600 interest per year?
let
x = amount invested at 14%
Interest earned in one year on this investment is 0.14x dollars.
Amount invested at 16% is 25000x
Interest earned in one year on this investment is 0.16(25000x) = 40000.16x dollars.
we want to find x in order to make at least $3,600 interest per year that is
interest for the part at 14% + interest for the part 16% >= total interest $3600
0.14*x + 4000  0.16*x >=3600
0.02*x >=400 multiply both sides by (1)
x <= $20,000
$20,000 is the most that can be invested at 14% in order to make at least $3,600 interest per year.
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