A shopkeeper marks his goods 20% above cost price, but allows 30% discount for cash payment. His net loss is ?

Answer: Option C

Let the cost price of goods = Rs. 100
Market price of goods
$$\begin{array}{rl}& \text{ = 120}\%\text{ of 100 }\\ & \text{ = }\frac{120}{100}\times \text{100}\\ & \text{ = Rs}\text{. 120}\end{array}$$
After discount selling price of goods
= 70% of 120
= Rs. 84
$$\begin{array}{rl}& \text{Loss = 100}-84=\text{Rs}\text{.16}\\ & \text{Loss }\%\text{ = }\frac{16}{100}\times 100=16\%\end{array}$$

Alternate :
$$\begin{array}{rl}& \text{Formula = }x\pm y\pm \frac{x\times y}{100}\\ & \text{Loss}\%\text{ = 20}-\text{30}-\frac{20\times 30}{100}\\ & =-10-6\\ & =-16\%(\text{Loss)}\end{array}$$