a) Rs. 1856.40
b) Rs. 1600
c) Rs. 1856
d) Rs. 1756.60

Answer: a
Explanation:
$$\eqalign{ & {\text{10}}\% {\text{ = }}\frac{1}{{10}} \cr & {\text{Principal}}\,\,\,\,\,\,\,{\text{Amount}} \cr & \,\,\,\,\,\,\,{\text{10}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,11 \cr & \,\,\,\,\,\,\,{\text{10}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,11 \cr & \,\,\,\,\,\,\,{\text{10}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,11 \cr & \,\,\,\,\,\,\,{\text{10}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,11 \cr & \underbrace {\overline {\,\,\,10000\,\,\,\,\,\,{\text{:}}\,\,\,\,\,{\text{14641}}\,\,\,} }_{{\text{CI = 4641}}} \cr & {\text{Principal = 10000 units}} \cr & {\text{ = Rs}}{\text{. 4000 (given)}} \cr & {\text{1 unit = }}\frac{2}{5} \cr & {\text{CI = 4641 unit}} \cr & {\text{ = Rs}}{\text{. }}\left( {\frac{2}{5} \times 4641} \right) \cr & = {\text{Rs}}{\text{. }}1856.40 \cr} $$