Find the principal which will amount to ₹ 4,000 in 4 years at 6.25% per annum.

Given:

A = ₹ 4,000

R = 6.25%

T = 4 years

Let the Principal amount be ₹ $P$.

As we know, $\text{A = S.I. + P}\\[1em] \Rightarrow 4,000 = \text{S.I. + P}\\[1em] \Rightarrow \text{S.I.} = 4,000 - P \\[1em]$

$\because \text{S.I.} = ₹ \Big(\dfrac{P \times R \times T}{100}\Big)\\[1em] \Rightarrow 4,000 - P = \Big(\dfrac{P \times 6.25 \times 4}{100}\Big)\\[1em] \Rightarrow 4,000 - P = \dfrac{P \times 25}{100}\\[1em] \Rightarrow 4,000 - P = \dfrac{P}{4}\\[1em] \Rightarrow 4,000 = \dfrac{P}{4} + P\\[1em] \Rightarrow 4,000 = \dfrac{P}{4} + \dfrac{4P}{4}\\[1em] \Rightarrow 4,000 = \dfrac{(P + 4P)}{4}\\[1em] \Rightarrow 4,000 = \dfrac{5P}{4}\\[1em] \Rightarrow P = \dfrac{4,000 \times 4}{5}\\[1em] \Rightarrow P = \dfrac{16,000}{5}\\[1em] \Rightarrow P = 3,200$

Hence, the Principal amount be ₹ 3,200.