# What is simple rule of three?

## What Does simple rule of three Mean

The rule of three is a mechanism that allows the resolution of problems related to the proportionality between three known values ​​and a fourth that is unknown . Thanks to the rule , the value of this fourth term can be discovered.

It is also important to be clear about other aspects of the aforementioned simple rule of three. We are referring to the fact that the problems it allows to solve are both direct and inverse proportionality. And this without forgetting either that to carry out one you must have three fundamental data: two magnitudes that are proportional to each other and a third.
In other words, a rule of three is an operation that is performed to find the value of the fourth term of a proportion from the values ​​of the other terms. According to its characteristics, it is possible to differentiate between the simple rule of three and the compound rule of three .

The simple rule of three is one that allows establishing the link of proportionality between two known terms ( A and B ) and, from the knowledge of a third term ( C ), calculating the value of the fourth ( X ).
Let's look at an example . A cook who, days ago, prepared three cakes with one kilogram of flour, now has five kilograms of flour and wants to know how many cakes he can make. To perform the calculation, apply the simple rule of three:
If with 1 kilogram of flour he prepared 3 cakes,

with 5 kilograms of flour he will prepare X cakes.
1 = 3

5 = X
5 x 3 = 1 x X

15 = X

In this way, the cook discovers that, with 5 kilograms of flour , he can prepare 15 cakes .
The simple rule of three can be direct or inverse. In the case of the simple direct rule of three , proportionality is constant: an increase in A corresponds to an increase in B in the same proportion.
An example to understand this type of simple rule of three would be the following: in a store we want to buy some chairs and they tell us that they sell them in packs. Specifically, they tell us that 5 are worth 600 euros, but we need 8 and we want to know what the price would be. Thus, to know the result we should carry out the following operations: 600 x 8 and the result, 4800, divide it by 5. Thus we would know that the eight chairs are worth 960 euros.
In the inverse rule of three simpler , however, the proportionality constant is only preserved when an increase of A , corresponds a decrease in B .
An example to understand how the simple inverse rule of three works is this: today a freight company has floated three trucks to transport a certain number of packages on six trips each. However, yesterday, to move the same number of packages, there were only two trucks of the same dimensions and capacities. So we are faced with the question of how many trips did these two vehicles make?

To find out, the operation would consist of doing these steps: 3 x 6 and the result, 18, dividing it by 2, which would give us that the two trucks had to make 9 trips each.

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