SOLUTION: a total of 30,000 is deposited, with equal amounts in 5% and 7% accounts and the balance in a 9% account. After two years, the total interest is 4,920. How much was deposited into

Question 987447: a total of 30,000 is deposited, with equal amounts in 5% and 7% accounts and the balance in a 9% account. After two years, the total interest is 4,920. How much was deposited into each account?
Answer by macston(5194) (Show Source): You can put this solution on YOUR website!
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F=x=amount in 5% account; S=x=amount in 7% account; N=amount in 9% account
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F+S+N=30000
x+x+N=30000
N=30000-2x
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Interest per year=4920/2=2460
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0.05F+0.07S+0.09N=2460
0.05x+0.07x+0.09(30000-2x)=2460
0.12x+2700-0.18x=2460
-0.06x=-240
x=4000
F=x=4000 ANSWER 1: 4000 was invested at 5%.
S=x=4000 ANSWER 2: 4000 was invested at 7%.
N=30000-2x=22000 ANSWER 3: 22000 was invested at 9%.
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CHECK:
0.05F+0.07S+0.09N=2460
0.05(4000)+0.07(4000)+0.09(22000)=2460
200+280+1980=2460
2460=2460
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