SOLUTION: Billy invested in a savings account for 3 years and was paid an annual rate of 4%. The total interest that he earned was $72. How much did he invest?

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Question 1207198: Billy invested in a savings account for 3 years and was paid an annual rate of 4%. The total interest that he earned was $72. How much did he invest?
Answer by MathLover1(20850)   (Show Source): You can put this solution on YOUR website!

Find the principal by using the formula
, where is interest, is total principal, is rate of interest per year, and is total time in years

In this example , % = and years, so
....solve for
...substitute given




Billy invested $.

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