Goods were bought for Rs. 600 and sold the same for Rs. 688.50 at a credit of 9 months and thus gaining 2% The rate of interest per annum is:

$$\eqalign{ & {\text{S}}{\text{.P}}{\text{.}} = 102\% \,of\,Rs.\,600 \cr & = {\frac{{102}}{{100}} \times 600} \cr & = Rs.\,612 \cr & {\text{Now,}}\,\cr & {\text{P}}{\text{.W}}{\text{. = Rs}}{\text{. 612}}\,{\text{and}}\,{\text{sum}} = Rs.\,688.50 \cr & \therefore {\text{T}}{\text{.D}}{\text{.}} = Rs.\,\left( {688.50 - 612} \right) \cr & = Rs.\,76.50. \cr & {\text{Thus,}}\,{\text{S}}{\text{.I}}{\text{.}}\,{\text{on}}\,{\text{Rs}}{\text{.}}\,{\text{612}}\,{\text{for}}\,{\text{9}}\,{\text{months}}\,{\text{is}}\,{\text{Rs}}{\text{.}}\,{\text{76}}{\text{.50}}{\text{.}} \cr & \therefore {\text{Rate}} = \left( {\frac{{100 \times 76.50}}{{612 \times \frac{3}{4}}}} \right)\% \cr & = 16\frac{2}{3}\% \, \cr} $$