A calculator says,
a) account balance: $208.12, so interest earned = $8.12
b) account balance: $1040.60, so interest earned = $40.60
c) account balance: $83,248.32, so interest earned = $3,248.32
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The compound interest multiplier for one year is (1 +r/n)^n, where r is the annual rate and n is the number of compoundings in a year. For this problem, you have r=.04, n=4.
a) account balance: $208.12, so interest earned = $8.12
b) account balance: $1040.60, so interest earned = $40.60
c) account balance: $83,248.32, so interest earned = $3,248.32
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The compound interest multiplier for one year is (1 +r/n)^n, where r is the annual rate and n is the number of compoundings in a year. For this problem, you have r=.04, n=4.