Step 1: Understanding Cost Price and Selling Price
The Cost Price (CP) is the price at which an item is purchased.
The Selling Price (SP) is the price at which the item is sold.
Step 2: Identifying the given values
\[ CP = Rs. 21000, \quad SP = Rs. 18900. \]
Step 3: Calculating Loss
Loss occurs if the selling price is less than the cost price: \[ \text{Loss} = CP - SP = 21000 - 18900 = Rs. 2100. \]
Step 4: Calculating Loss Percentage
Loss percentage is given by: \[ \text{Loss %} = \left( \frac{\text{Loss}}{CP} \right) \times 100 = \left( \frac{2100}{21000} \right) \times 100 = 10%. \]
Step 5: Conclusion
The person incurred a loss of 10%.