Question 1203605
If an amount of $9,000 is invested at a simple interest rate of 3 1/2% interest per year, 
how much additional money (in dollars) must be invested at a simple interest rate of 5% per year 
to ensure that the interest each year is 4% of the total amount invested?
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Let x be the value under the problem question (= an additional amount to invest at 5%).


From one side, these two amounts of $9000 and x dollars generate the total annual interest
of 0.035*19000 + 0.05x  dollars.


From the other side, we want to have the total annual interest of 0.04(9000+x)  dollars.


So, we write this equation

    0.035*9000 + 0.05x = 0.04(9000+x)   dollars.


Now simplify and find x

    0.035*9000 + 0.05x = 0.04*9000 + 0.04x

    0.05x - 0.04x = 0.04*9000 - 0.035*9000

        0.01x     =       45

            x     =       45/0.01 = 4500.


<U>ANSWER</U>.  An additional amount to invest at 5% is 4500 dollars.
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Solved.