Q.At what principal will the amount be ₹13,310 in 3 years at 10% per annum, compounded yearly?

To find the principal, divide the given amount by $(1+r/100)^t$.

Here $A = ₹13{,}310$, $r = 10\%$, $t = 3$ years, compounded yearly. The formula $A = P(1+r/100)^t$ must be solved for $P$.

Step 1 — Rearrange for $P$.

Step 2 — Evaluate $(1.1)^3$. $(1.1)^3 = 1.331$.

Step 3 — Divide.

$P = \frac{13{,}310}{1.331} = ₹10{,}000$ …

Multiplying $A$ by $(1+r/100)^t$ instead of dividing by it is a common inversion error — always check the direction of the formula: the amount is always larger than the principal for positive interest, so a co …