The difference between CI and SI on a certain sum of money at 10% per annum for 3 years is Rs. 620. Find the principal if the interest is compounded annually.

Suppose principal is Rs. $P$

$r = 10%, t = 3$ years and $[CI – SI] =$ Rs. $620$

620 = P[1 + 10/100]³ – P – [P × 10 × 3]/100

$620 = 1.331P – P – 0.3P$

$0.031P = 620$

$P = 20000$

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