A merchant allows a discount of 10% on marked price for the cash payment. To make a profit of 17%, he must mark his goods higher than their cost price by = ?

$$\eqalign{ & {\text{Let the cost price = Rs}}{\text{. 100}} \cr & {\text{Selling price }} \cr & {\text{ = 117}}\% {\text{ of 100 }} \cr & {\text{ = Rs}}{\text{. 117}} \cr & {\text{Marked price}} \cr & {\text{ = 117}} \times \frac{{100}}{{90}}{\text{ }} \cr & {\text{ = Rs}}{\text{. 130}} \cr & {\text{Marked price above }}\% \cr & = \frac{{130 - 100}}{{100}} \times 100\% \cr & = 30\% \cr} $$