Assuming a cost price of Rs. 100 for 1 kg, the selling price is set at 90\% of the cost, equating to Rs. 90 per kg. However, the dealer uses only 0.7 kg due to a 30\% reduction in weight.
The selling price for 0.7 kg is Rs. 90, while the cost price remains Rs. 100 for the original 1 kg. The profit percentage is calculated as \[ \frac{90 - 100}{100} \times 100 = 28 \frac{4}{7} \% \text{ profit.} \]