there are two investments, x and y, that total $25,000......that is, x + y = 25,000
let x be the amount invested at 6% and let y be the amount invested at 9%, the total annual percentage from these two investments equals $2,070......that is, 0.06x + 0.09y = 2,070
notice that you must convert from percent form to decimal form because a percentage is out of 100 parts, (for example, 6 out of 100 is 6% so 6%/100% = 6/100 = 0.06)
thus, the system contains the following 2 equations:
(1.) x + y = 25,000
(2.) 0.06x + 0.09y = 2,070
first, you want to eliminate one of the variables and solve for the other, then plug in the number for the variable you solved for to find the other variable...
let's solve for x first, so we want to eliminate y to do that.....multiply equation (1.) by -0.09 then add it to equation (2.):
(1.) x + y = 25,000 ===> -0.09 (x + y = 25,000) ===> -0.09x - 0.09y = -2,250
(2.) 0.06x + 0.09y = 2,070
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-0.03x + 0y = -180
so, -0.03x = -180 (divide both sides by -0.03) ===> (-0.03/-0.03)x = -180/-0.03 ===> x = 6,000
plug x back into one of the main equations (the first one would be the easiest) and solve for y:
x + y = 25,000 ===> 6,000 + y = 25,000 (subtract 6,000 from both sides)
-6,000 -6,000
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0 + y = 19,000 ===> y = 19,000
so, the amount invested at 6% (x) was $6,000 and the amount invested at 9% (y) was $19,000
Plug these #s back into equation (2.) to check:
0.06x + 0.09y = 2,070 ===> 0.06(6,000) + 0.09(19,000) = 360 + 1,710 = 2,070
Jeff C.
I think you're probably right. Well done!10/10/12