Final answer:
The merchant made a loss of Rs 100 by buying a quintal of potatoes for Rs 4,000 and selling them at Rs 390 per 10 kg.
Step-by-step explanation:
The question is about calculating the profit or loss made by a merchant who bought a quintal (100 kg) of potatoes for Rs 4,000 and sold all of them at Rs 390 per 10 kg. To calculate this, we need to determine the total selling price and then subtract the cost price from this selling price.
First, we'll calculate the selling price for the entire quintal. Since the merchant sells potatoes at Rs 390 per 10 kg, for 100 kg, which is one quintal, the total selling price would be Rs 390 multiplied by 10 (because 100 kg is 10 times 10 kg). Therefore, the selling price is Rs 3,900.
To find out the profit or loss, we subtract the cost price (Rs 4,000) from the selling price (Rs 3,900). Thus, we get a loss of Rs 100 (4000 - 3900).