The problem:
A shopkeeper sells his goods at cost price but uses a weight of 900 grams instead of 1 kilogram. We need to calculate the shopkeeper's gain percentage.

Solution:
To solve this problem, we need to understand the concept of gain and gain percentage.

Gain:
Gain is the difference between the selling price and the cost price of an item. In this case, the shopkeeper is selling the goods at cost price, so there is no gain.

Gain Percentage:
Gain percentage is the percentage increase in the cost price of an item. It is calculated using the formula:
Gain percentage = (Gain ÷ Cost price) × 100

Since there is no gain in this case, the gain percentage will be zero.

Explanation:
The shopkeeper is selling the goods at cost price, which means he is not making any profit. However, he is using a weight of 900 grams instead of 1 kilogram. This means that the customer is getting 100 grams less for every kilogram of goods purchased.

To calculate the gain percentage, we need to compare the cost price of the goods using the actual weight (1 kilogram) and the weight the shopkeeper is using (900 grams).

Let's assume the cost price of 1 kilogram of goods is $100. Using this assumption, we can calculate the cost price for 900 grams of goods.

Cost price for 1 kilogram = $100
Cost price for 900 grams = (900/1000) × $100 = $90

Now, let's calculate the gain percentage using the formula:

Gain percentage = (Gain ÷ Cost price) × 100
= (0 ÷ $90) × 100
= 0%

So, the shopkeeper's gain percentage is 0%. He is selling the goods at cost price, but by using a weight of 900 grams instead of 1 kilogram, he is effectively reducing the quantity the customer receives without increasing the price. This is a dishonest practice as the customer is not getting the full value for their money.

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