Cost Price– the price of which an article is purchased is called its cost price(CP)
Selling Price– the price at which on article is sold , is called its selling price (SP)
Profit or Gain– if SP is greater than CP , the seller is said to have a profit.

Loss- if SP is less than CP the seller is said to have is called a loss.

Calculation

If an article is sold at a gain of say then

If an article is sold at a loss of say than

When a person sells two similar items one at a gain of say x% & the other at a loss of x% than the seller always increase a loss given by

If a trader professes to sell his goods at cost price but uses false weight than

Example
If pure ghee costs Rs 100/kg after adulterating it with vegetable oil casting Rs 50/kg a profit of 20% in what ratio does he mix the two.

Required ratio- 30:20
Oil: ghee