PreAlgebra and Algebra Formulas You Must Know for the ACT
Some of the questions on the ACT Math test deal with prealgebra and algebra problems. There are only a few formulas to remember, but they are vital.
Here are two important prealgebra formulas you need to know:
Here are three useful algebra formulas:

Direct proportionality. Two variables, x and y, are directly proportional when the following equation is true for some constant k:

Inverse proportionality. Two variables, x and y, are inversely proportional when the following equation is true for some constant k:

The quadratic formula. For any quadratic equation — that is, an equation of the form ax^{2} + bx + c = 0 — the value of x is as follows: