A discount of 10% is given by a salesman for cash payment. What should be the marked price if he wants to earn a profit of 5% ?

$$\eqalign{ & \,\,\,{\text{Cost price}}:{\text{Marked price}} \cr & \left( {100 - {\text{D}}\% } \right):\left( {100 + {\text{P}}\% } \right) \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\underbrace {90\,\,\,\,\,\,\,\,\,\,{\text{:}}\,\,\,\,\,\,\,\,\,\,\,{\text{105}}}_{15} \cr} $$
Percentage of marked price above cost price
$$\eqalign{ & = \frac{{15}}{{90}} \times 100 \cr & = 16\frac{2}{3}\% \cr & = 16.67\% \cr} $$