On what sum will the compound interest for 2 years at 4% per annum be ₹5712?

Let principal = P,

C.I. = $P\Big[\Big(1 + \dfrac{r}{100}\Big)^n - 1\Big]$

Putting values in formula we get,

$\Rightarrow 5712 = P\Big[\Big(1 + \dfrac{4}{100}\Big)^2 - 1\Big] \\[1em] \Rightarrow 5712 = P\Big[\Big(\dfrac{104}{100}\Big)^2 - 1\Big] \\[1em] \Rightarrow 5712 = P\Big[\Big(\dfrac{26}{25}\Big)^2 - 1\Big] \\[1em] \Rightarrow 5712 = P\Big[\dfrac{676}{625} - 1\Big] \\[1em] \Rightarrow 5712 = P\Big[\dfrac{676 - 625}{625}\Big] \\[1em] \Rightarrow 5712 = P \times \dfrac{51}{625} \\[1em] \Rightarrow P = \dfrac{5712 \times 625}{51} \\[1em] \Rightarrow P = 112 \times 625 \\[1em] \Rightarrow P = ₹70000.$

Hence, principal = ₹70000.