Rs. 64,000 will amount to Rs. 68,921 at 5% per annum and interest payable half yearly in

mount = Rs. 68921

Principal = Rs. 64000;

Rate $=frac{5}{2} \%$ per half year

$A=Pleft(1+frac{R}{100} ight)^{T}$

$Rightarrow 68921=64000left(1+frac{5}{200} ight)^{T}$

$Rightarrow frac{68921}{64000}=left(1+frac{1}{40} ight)^{mathrm{T}}$

$Rightarrowleft(frac{41}{40} ight)^{3}=left(frac{41}{40} ight)^{mathrm{T}}$

$Rightarrow mathrm{T}=3$ half years $=1 frac{1}{2}$ years