A total of $5000 is invested at 2%, 3% and 4%. The amount invested at 4% equals the total amount invested at 2% and 3%. The total interest for one years is $145. If possible, find the amount invested in each interest rate. Interpret your answer.
Let x=the amount invested at 2%
y=the amount invested at 3%, and
z=the amount invested at 4%,
We know the total of all three investments is $5000, so
The amount invested at 4%, z, equals the total amount invested at 2% and 3%, so
Assume the interest is compounded annually, then
We now have three equations and three unknowns!
First eliminate z by substituting  into  then  into :
We now have two equations and two unknowns, x and y:
From , y=2500-x. Substitute this into :
Since a negative investment, y, makes no sense, my assumption about the compounding period could be wrong.
I showed all steps so those a little weak with algebra can follow the solution.