The present worth of a certain sum due sometime hence is Rs. 3400 and the true discount is Rs. 340. The banker's gain is:

Solution (By Examveda Team)

$$\eqalign{ & BG = \frac{{{{(TD)}^2}}}{{PW}} \cr & \,\,\,\,\,\,\,\,\,\,\, = \frac{{{{(340)}^2}}}{{3400}} \cr & \,\,\,\,\,\,\,\,\,\,\, = \frac{{340 \times 340}}{{3400}} \cr & \,\,\,\,\,\,\,\,\,\,\, = \frac{{340}}{{10}} \cr & \,\,\,\,\,\,\,\,\,\,\, = {\text{Rs}}{\text{.}}\,34 \cr} $$