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SubstituteTechnique

Technique

Substitute

Swap in the value, parentheses and all

3 min 3 steps

A substitute has to fit exactly where the original stood. I once sent a stand-in to roll call, and the details gave us away.

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Used by

Backsolve from the choicesTacticTest the middle choice, then step up or down
Plug in concrete numbersTacticSwap letters for numbers, then match the choice
Solve a system of two linear equationsTacticCancel one variable, then answer what's asked
Build a linear function from two factsTacticSlope from the change, intercept from one point
Evaluate, invert, and transformTacticFind the missing end, then let the slope carry changes
Solution-count and discriminant analysisTacticCollect everything on one side, then read one sign
Solve a nonlinear systemTacticSubstitute, keep every root, then find each y
Evaluate, compose, and transformTacticSubstitute the whole input, parentheses and all
Set up a proportion or unit rateTacticLabel every rate with units, then match or cancel them
Percent change, chains, and reverseTacticMultiply forward, divide back, never add percents
Reason about center and spreadTacticMeans follow the total, medians follow the middle