Subtract, Then Divide
Part of the Fundamentals section of Coddy's Algebra journey. Lesson 18 of 64.
In 3x + 5 = 20, the unknown is multiplied by 3 and then 5 is added. Undo the operations in reverse order. Subtract 5 from both sides, then divide both sides by 3:
3x = 15
x = 5
Check: 3 × 5 + 5 = 20, which is true.
In a two-step equation, each number is undone by a different operation. You subtract the 5, because it was added. You divide by the 3, because it is the coefficient. The 20 only changes through the arithmetic on the right side. If the order is unclear, say the equation in words: three times a number, plus five, is twenty.
Challenge
EasySolve the equation 41 = 6x + 5 for x.
Try it yourself
Solve for x
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Fundamentals
1What an Equation Is
The EquationFinding the UnknownThe Same to Both SidesSolved Means AloneRecap: First Equations4Two-Step Equations
Two Layers to UndoSubtract, Then DivideAdd, Then DivideA Division InsideNegatives in Two StepsRecap: Two-Step Equations2One-Step Equations
Undoing AdditionUndoing SubtractionUndoing MultiplicationUndoing DivisionInverse OperationsRecap: One-Step Equations5Tidying First
Like TermsTerms and Numbers MixedThe Distributive PropertyDistributing a SubtractionTidy, Then SolveRecap: Tidying First