What sum of money will amount to Rs 21296 in 3 years at 10%

Let $P$ be the sum.

Rate of interest, $R=10 \%$

Time, $n=3$ years

Now, $A=P \times\left(1+\frac{10}{100}\right)^{3}$

$=$ Rs. $P \times\left(\frac{100+10}{100}\right)^{3}$

$=$ Rs. $P \times\left(\frac{110}{100}\right)^{3}$

$=$ Rs. $P \times\left(\frac{11}{10} \times \frac{11}{10} \times \frac{11}{10}\right)$

$=$ Rs. $\frac{1331 P}{1000}$

However, amount $=$ Rs. 21296

Now, Rs. $21296=$ Rs. $\frac{1331 P}{1000}$

$\Rightarrow$ Rs. $\left(\frac{21296 \times 1000}{133}\right)=P$

$\therefore P=$ Rs. 16000

Hence, the required sum is Rs. 16000 .