Quarterly compound interest evaluated without a calculator using a binomial expansion

Quarterly compound interest evaluated without a calculator using a binomial expansion

7 marks

A deposit of \(3000\) dollars is placed in a savings account. Interest is added every three months at a nominal rate of \(12\%\) per annum. At the end of the first year, the account holds \(3000(1+k)^4\) dollars, where \(k\) is a rational number.

  1. Write down \(k\).[1]
  2. Expand and simplify \((1+x)^4\).[2]
  3. Hence or otherwise, find, to the nearest dollar, the balance of the account at the end of the first year.[4]

Solution:

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Answer:(a) \(k=0.03\) (b) \(1+4x+6x^2+4x^3+x^4\) (c) \(3377\) dollars

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