a) Rs. 10 loss
b) Rs. 10 profit
c) Rs. 90 loss
d) Rs. 90 profit

Answer: a
Explanation: Selling price of a radio (SP) = Rs 990
profit (g) = 10%
Let the cost price = CP
$$\eqalign{ & {\text{CP}} = \frac{{{\text{SP}} \times 100}}{{100 + {\text{g}}}} \cr & \Rightarrow CP = \frac{{990 \times 100}}{{100 + 10}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{990 \times 100}}{{110}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = {\text{Rs}}{\text{.}}\,900 \cr & {\text{CP}} = Rs.\,900 \cr & {\text{SP}} = Rs.\,890 \cr & {\text{CP}} > {\text{SP}} \cr & {\text{He}}\,{\text{gets}}\,{\text{loss}} \cr & = {\text{Rs}}{\text{.}}\,900 – {\text{Rs}}{\text{.}}\,890 \cr & = {\text{Rs}}{\text{.}}\,10 \cr} $$