A dishonest dealer professes to sell goods at the cost price, but uses a false weight of 900 grams instead of a kg. His gain percentage is:

Correct option is C

Given:

The dealer uses a false weight of 900 grams instead of 1 kg (1000 grams).

He sells goods at the professed cost price (i.e., he sells 900 grams for the price of 1000 grams).

Formula Used:

Gain Percentage = $$\frac{\text{Gain}}{\text{Cost Price}} \times 100$$​​

Solution: 

Here, the gain is the difference in weight, which is 100 grams (1000 grams - 900 grams), and the cost price is based on 900 grams.

The dealer gives 900 grams but charges for 1000 grams. Hence, the gain is:

Gain = 1000 grams − 900 grams = 100 grams

The dealer sells 900 grams for the cost of 1000 grams. The gain percentage is:

Gain Percentage = $$\frac{100}{900} \times 100 = \frac{100}{900} \times 100 = 11\frac{1}{9}$$​%

Thus, the dealer's gain percentage is $$11\frac{1}{9}$$​%.