SOLUTION: Billy invests $12,000. Part of it at 4% intrest and the rest at 5.5%. If his interest was $532.50 how much did he invest at each rate?

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Question 353616: Billy invests $12,000. Part of it at 4% intrest and the rest at 5.5%. If his interest was $532.50 how much did he invest at each rate?
Answer by JBarnum(2146)   (Show Source): You can put this solution on YOUR website!
all these money type problems are set up the same way once u get used to seeing the pattern then you wont have trouble figuring out what needs to be done


total=$12000
to get total add both portions x+y
so
4%=.04 and 5.5%=.055
the total interest amount is $532.50
so


So you have now found your 2 equations to bea ble to solve this problem, once you get used to doing these this process to finding the equations will come naturally.



You can solve by elimination or by substitution whichever you find more comfortable using, I like Elimination method as it is much faster.
multiply by .055

.

subtract equations
-------------------------
divide by .015
this is the portion at 4% interest


Now instead of doing that whole process over to find "y" simply plug in the value of "x" in the equation

this is the portion at 5.5% interest

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