Many everyday calculations can be easily solved with the rule of three calculator. First, it's important to determine whether the relationship is direct or inversely proportional.
Direct: If one quantity changes in the same direction as another, the relationship is direct, i.e., 'the more, the more' or 'the less, the less'. The arrow points downwards. Example: The more units of a product are purchased, the higher the bill. Or: The fewer hours worked, the less brickwork is completed. etc.
Inversely Proportional: The opposite is true if the relationship is inversely proportional, i.e., 'the more, the less' or 'the less, the more'. The arrow points upwards. Example: The higher the loading capacity of a truck, the fewer trips are needed to achieve a certain delivery rate. Or: The slower the vehicle is driven, the more time it takes to cover a certain distance.
In addition to simple relationships, this calculator can also be used to solve complex relationships. Example: If 10 workers work 8 hours a day, they complete a task in 10 days. How long would it take 7 workers to complete the same task if they worked 10 hours a day?
In the rule of three calculator, the same units are always written one below the other in the fields. The direction of the arrows next to them indicates whether the relationship is direct (downward arrow) or inverse. The last arrow always points downward, i.e., towards the unknown quantity.
Simple rule of three:
Example 01: Three lamps cost 12 euros. How much do 10 lamps cost?
The relationship is proportional, so changing the arrow direction is not necessary.
known majority: Enter 3 in the first field and 12 in the field next to it.
new majority: Enter 10 in the first field.
Click 'calculate'. The result will appear in the fourth field.
Example 02: To transport the excavated material, 4 truck trips are needed if each truck has a 5-ton capacity. How many trips would be needed with a truck with a 2.5-ton capacity?
The relationship is inversely proportional, so click on the two circular arrows to change the direction of the arrows to inversely proportional.
Given majority: Enter 5 in the first field and 4 in the field next to it.
New majority: Enter 2.5 in the first field.
Click 'calculate'. The result will appear in the fourth field.
Double rule of three:
If you have a double proportion problem, click on ||>. Two additional fields will appear. Enter the data as described above.
Example 03: If 10 workers work 8 hours a day, they complete a job in 10 days. How long would it take 7 workers to complete the same job if they worked 10 hours a day?
Click on ||> to display the two additional fields.
Both relationships are inversely proportional to the quantity we are looking for, because 'the more workers, the fewer days' and 'the more hours per day, the fewer days'.
Both arrows must therefore point upwards. Click on the respective circular arrows to reverse the arrows.
Given majority: Enter 10 in the first field, 8 in the second field, and 10 in the third field.
New majority: Enter 7 in the first field and 10 in the field next to it.
Click 'calculate'. The result will be entered in the empty field.
Note: Of course, the rule of three can also be proportional, or one quantity can be proportional and the other inversely proportional.
