# Pre-Algebra and Algebra Formulas You Must Know for the ACT

from ACT Math For Dummies

Some of the questions on the ACT Math test deal with pre-algebra and algebra problems. There are only a few formulas to remember, but they are vital.

Here are two important pre-algebra 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: