Frequent use of expressions that reflect increases or decreases in prices, numbers or quantities, always based on 100 units. Some examples:

  • Gasoline increased by 15%.
    It means that every $ 100 there was an increase of $ 15.00.

  • The customer received a 10% discount on all goods.
    This means that for every $ 100 a discount of $ 10 was given.

  • Of the players who play at Grêmio, 90% are star players.
    It means that out of every 100 players who play at Grêmio, 90 are stars.

Centesimal reason

All the reason that has for the number 100 consequent is denominated centesimal reason. Some examples:

We can represent a centesimal ratio in other ways:

The expressions 7%, 16% and 125% are called centesimal rates or percentage rates.

Consider the following problem:

John sold 50% of his 50 horses. How many horses did he sell?

To solve this problem, we must apply the percentage rate (50%) on the total horses.

Soon he sold 25 horses, which represents the percentage wanted. So we come to the following definition:

Percentage is the value obtained by applying a percentage rate to a given value.


  • Calculate 10% of 300.

  • Calculate 25% of 200kg.

    Therefore, 50kg is the value corresponding to the percentage sought.


1) A soccer player over a championship charged 75 fouls, turning 8% of those fouls into goals. How many foul goals has this player scored?

Therefore the player made 6 foul goals.

2) If I bought a club stock for $ 250 and resold it for $ 300, what is the percentage rate of profit earned?

We set up an equation, where adding the initial $ 250.00 with the percentage that increased from that $ 250.00, results in the $ 300.00.

Therefore, the percentage rate of profit was 20%.

Next: Multiplication Factor