SOLUTION: Doc O had 10,000 invested at 5%. How much would he have to invest at 8% so that his total interest per year would equal 7% of the two investments?

Question 104922: Doc O had 10,000 invested at 5%. How much would he have to invest at 8% so that his total interest per year would equal 7% of the two investments?
Answer by edjones(8007) (Show Source): You can put this solution on YOUR website!
Let x= how much he would hav to invest at 8%.
10000*.05+.08x=.07(10000+x)
500+.08x=700+.07x
.01x=200 subtract .07x+500 from each side.
x=200/.01= $20,000. divide each side by .01
Check:
10000*.05+20000*.08=500+1600=$2,100.
30000*.07=$2,100.
Ed

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