Question 1151774
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Chart
<img src = "https://i.imgur.com/LQeyLOO.png">
In the bottom row, the highlighted cells will help us form an equation to solve for x.
The product of the blue and green cells is 
(15000+x)*0.08
or
0.08(15000+x)
Note how I'm using the decimal form of 8%


The product of the blue and green cells is equal to the yellow cell, which is the total profit we want. 


Solve for x
0.08(15000+x) = 1500+0.03x
0.08(15000)+0.08(x) = 1500+0.03x
1200+0.08x = 1500+0.03x
0.08x-0.03x = 1500-1200
0.05x = 300
x = 300/0.05
x = 6000


<font color=red>Answer: Lucy will need to invest $6,000 in fund B.</font>


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Check:


The total amount invested is 15,000+6,000 = 21,000
Take 8% of this: 0.08*21,000 = 1,680


Fund A returns 10% on $15,000 invested, so it returns 0.10*15,000 = $1,500
Fund B returns 3% on $6,000 invested, so it returns 0.03*6000 = $180
In total, 1500+180 = 1680 is returned, which matches with the result we got above.


Here is the updated chart
<img src = "https://i.imgur.com/Xgh9VBF.png">
Side note: it does not make sense to add the percentages for funds A and B
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