A shopkeeper buys $12$ chocolates for ₹ $6$. To gain a $20\%$ profit, how many chocolates should he sell for ₹ $6$?

Cost Price (CP) of $12$ chocolates = ₹ $6$
CP of $1$ chocolate $=\frac{6}{12}=₹0.5$

Desired profit $=20\%$
Selling Price (SP) of $1$ chocolate $=\text{CP}\times (1+\frac{\text{Profit\%}}{100})$

$$\text{SP}=0.5\times (1+\frac{20}{100})=0.5\times 1.2=₹0.6$$

Now, we need to find how many chocolates he should sell for ₹ $6$ at this rate.

$$\text{Number of chocolates}=\frac{\text{Total SP}}{\text{SP per chocolate}}$$

$$\text{Number}=\frac{6}{0.6}=10$$