Rule Of Three Example

The rule of three it is one of the ways to solve mathematical problems of proportions. It is used to calculate an unknown number based on the relationship between two quantities or magnitudes.

The rule of three is used by ordering the known quantities separated by a colon (:) by placing the known quantity in the same place in relation to the colon (:) where the quantity or magnitude is similar; For example, if we represent by A and B some known quantities that have a relationship and we want to know the relationship when the quantity represented by A increases, which we will represent by A ’will be written So:

A: B = A ’:?

If the data we know is another quantity of B, which we will call B ', then it will be written like this:

A: B =?: B '

The data arranged in this way are identified in relation to the = sign, calling them the center to the closest ones, and the extreme to the far ones. To calculate the unknown, (that is, the unknown quantity), we will multiply the pairs of known data, in relation to the = sign, that is, in the first example those of the center and in the second example those of the extremes, and we will divide the result between the known data and the other member of the equation.

Rule of three example:

Problem:

If in six minutes and 11 seconds I have consumed 59 calories, how many calories will I consume in 10 minutes?

Step 1

First we order the data and to facilitate the operations we will convert the minutes to seconds:

Time = 371 seconds

Calories consumed = 59 calories

Time 2 = 600 seconds

Calories consumed = X

Data order: 371: 59 = 600: X

Step 2

As we know the quantities in the center (those closest to the = sign) we will multiply them:

59 x 600 = 35400

Step three

Now we will divide the result obtained by the known data:

35400 / 371 = 95.41778976

Therefore in 10 minutes 95.41778976 will be consumed

Another way to solve it:

If we order the same data in a different way, we will also get the same result:

59: 371 = X: 600

In this case we will multiply the extremes and divide by the known data of the center.

59 x 600 = 35400

35400 /371 = 95.41778976