Question 98721
Interest(I)=Principal(P) times Rate(R) times(T) or I=PRT
Let P=additional amount of principal needed to be deposited at 4%


0.06(15,000)=return for 1 year on the 15,000
0.04P=return for 1 year on the amount deposited at 4%
0.055(15000+x)=return for 1 year on the combined deposit
Now we know that the return on the two separate deposits must equal the return on the combined deposit.  So our equation to solve is:

0.06(15000)+0.04P=0.055(15000+P)  get rid of parens
900+0.04P=825+0.055P  subtract 825 and also 0.04P from both sides

900-825+0.04P-0.04P=825-825+0.055P-0.04P  collect like terms

75=0.015P  divide both sides by 0.015

P=$5000-----------additional amount of principal needed to be deposited at 4%

CK
0.06*15000+0.04*5000=0.055*20000
900+200=1100
1100=1100

Hope this helps----ptaylor