Subtract, Then Divide
Part of the Fundamentals section of Coddy's Math journey. Lesson 18 of 64.
3x + 5 = 20: the unknown is tripled and then 5 is added. Reverse order: subtract 5, then divide by 3.
3x = 15
x = 5
Check: 3 × 5 + 5 = 20. True.
Two-step equations are where the "which number?" question first bites: you subtract the 5 (the number added), and you divide by the 3 (the coefficient). Neither move touches the 20 except through the arithmetic. Say the equation in words if the order is unclear: "three times a number, plus five, is twenty".
Challenge
Solve 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