Question 34420: Walt made an extra $9000 last year from a part-time job. He invested part of the money at a 9% annual rate of interest, and the rest at an 8% annual rate of interest. At the end of the year, he made a total of $770 in interest. How much was invested at 8%?
Answer by hydromojo(20)   (Show Source):
You can put this solution on YOUR website! Lets say Walt puts $'X' @8%. the remaining would be $(9000-X)
Interest calculation = amount * (rate/100)0*time(in yrs in this case)
So, for the 8% investment
Interest = X * (8/100) * 1 = $.08X ........#1
for the 9% investment
Interest = (9000-X) * (9/100) * 1 = 810 - 0.09X ...........#2
The total interest is given as $770, so adding #1 & 2, we get
.08X + 810 - .09X = 770
solve this for X, and you get it to be $4000
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