Question

A sum when reckoned at 7½% per annum amounts to ¥3920 in 3 years. Find the sum.

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Answer 1

Answer:

$amount = p(1 + \frac{r}{100} ) {}^{n} \\ so \\ a = 3920(1 + \frac{7 \ \frac{1}{2} }{100} ) {}^{3} \\ \\ 7 \ \frac{1}{2} = \frac{15}{2} \\ \\ 3920(1 + \frac{15}{2 \times 100} ) {}^{3} \\ 3920(\frac{43}{40} ) {}^{3} \\ \frac{3920 \times 43 \times 43 \times 43}{40 \times 40 \times 40} \\ = 4869.80 \\ \\ compound \: interest \: = amount - principle \\ = 4869.80 - 3920 \\ = 948.80$

So, the compound interest is = ¥ 4869.80