Profit, Loss and percentage problem.

Question

A dishonest businessman professes to sell his articles at cost price but he uses false weight by which he cheats by 10% while buying and 10% while selling. find his profit percentage?

Answer 1

An item that should cost $1$ is bought for $0.9$ and sold for $1.1$. Do you define profit percentage on the buying price or the selling price?

Answer 2

Suppose that the original cost of the article is 100.

In the process of buying, he cheats by 10%. This means he only paid 90 for it.

He will sell it at his cost price (90), with a 10% cheating. This means he obtained a payment of 99.

Now, the (original) cost price is 90, and the (new) selling price is 99. Can you find the profit percent?