Solving for a Letter
Part of the Fundamentals section of Coddy's Algebra journey. Lesson 58 of 64.
Sometimes you want to rearrange a formula so that a different letter is on its own. From P = 2l + 2w, make a formula for w. Treat every other letter as if it were a known number, and undo what is done to w. Subtract 2l from both sides, then divide both sides by 2:
P - 2l = 2w
w = (P - 2l)/2
The result is a formula for the width in terms of the perimeter and the length. It is the same equation, solved for w instead of P.
Letters such as P and l stand for numbers that have not been given. To get the letter you want on its own, do the same operation to both sides, just as you would with numbers. If you divide both sides by an expression, that expression must not be zero.
Challenge
MediumRearrange d = st to give a formula for the time t.
Try it yourself
Solve for t
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