The application RegraD3 (App RegraD3) performs the mathematical operation of the Rule of Three Simple.

The Simple Three Rule is a procedure used to solve problems involving quantities that can be directly or inversely proportional. Examples:

DIRECT:
If a 269 ml can costs R $ 2.19 and a 473 ml can costs R $ 3.49, what is the most advantage to buy?
(R $ 2.19 x 473) / 269 = R $ 3.85, that is, 473 ml should cost R $ 3.85 and is costing R $ 3.49, R $ 0.36 less.

INVERSE:
If a car goes at 50 km / h and takes 10 minutes to reach the destination, if it travels the same path at 80 km / h, how long will it take? In this case, but speed takes less time, it is the inverse proportion, being like this:
(50 x 10) / 80 = 6.25. The value 6.25 converted to minutes is equal to 6 + (1/4 of 60 = 15 seconds), thus 6 minutes and 15 seconds.