Add, Then Divide
Part of the Fundamentals section of Coddy's Algebra journey. Lesson 19 of 64.
In 4x - 7 = 9, the unknown is multiplied by 4, and then 7 is subtracted. Undo the subtraction first by adding 7 to both sides. Then divide both sides by 4:
4x = 16
x = 4
Check: 4 × 4 - 7 = 9, which is true.
The sign in front of a number is part of that number. In 4x - 7, the second operation is minus 7, and the inverse of minus 7 is plus 7. If you read it as 7 and subtract, you get 4x = 2 and a wrong answer. Checking the answer in the original equation shows the mistake.
Challenge
EasySolve the equation 3x - 11 = 10 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