A dishonest shopkeeper uses two different scales while buying and selling the goods. Both the scales are faulty. While buying he uses a scale that shows 900 gm per kg of the goods bought. Similarly while selling, he uses a scale that shows 1100 gm per kg of the goods sold. What is his profit percent, if he claims to sell the goods at cost price?

Step 1: Understand the problem

The shopkeeper is using two different scales. When he buys goods, his scale shows 900 gm for every kg. This means he is actually getting more goods than he thinks because his scale is under-measuring. When he sells goods, his scale shows 1100 gm for every kg. This means he is actually giving less goods than he thinks because his scale is over-measuring. He claims to sell the goods at the same price he bought them for, which is known as the cost price.

Step 2: Calculate the actual weight of goods bought and sold

When the shopkeeper buys 1 kg of goods, he actually gets 1000/900 = 1.111 kg (because his scale under-measures). When he sells 1 kg of goods, he actually gives 1000/1100 = 0.909 kg (because his scale over-measures).

Step 3: Calculate the profit

The shopkeeper buys 1.111 kg of goods and sells 0.909 kg of the same goods for the same price. This means he still has 1.111 - 0.909 = 0.202 kg of goods left that he can sell to make a profit.

Step 4: Calculate the profit percentage

The profit percentage is the profit divided by the cost price, multiplied by 100. The cost price is the price of 1 kg of goods, and the profit is the price of 0.202 kg of goods. So the profit percentage is (0.202/1) * 100 = 20.2%.

So the shopkeeper makes a profit of 20.2% by using faulty scales and selling the goods at cost price.