A dishonest shopkeeper professes to sell goods at his cost price but uses a false weight of $960\text{gm}$ for each kilogram. What is his gain percent?

Let the cost price of $1000\text{gm}$ ($1\text{kg}$) of goods be ₹$1000$.
The shopkeeper sells $960\text{gm}$ of goods but claims it to be $1000\text{gm}$, charging the cost price of $1000\text{gm}$.

Therefore:

* Cost Price ($\text{CP}$) of the goods actually sold ($960\text{gm}$) = ₹$960$
* Selling Price ($\text{SP}$) of those goods = ₹$1000$

$$\text{Profit}=\text{SP}-\text{CP}=1000-960=40\text{gm (or ₹}40\text{)}$$

$$\text{Gain Percent}=\left(\frac{\text{Profit}}{\text{CP}}\right)\times 100\%$$

$$\text{Gain Percent}=\left(\frac{40}{960}\right)\times 100\%=\frac{1}{24}\times 100\%=\frac{25}{6}\%=4\frac{1}{6}\%$$