Plugging In Numbers for Algebra Problems

GRE Quantitative · Axiom Academy

When a problem is drowning in variables, trade the algebra for arithmetic — pick a number, work it out, and let the answer choices sort themselves. 1. Trade the Algebra for Arithmetic Say a problem defines one variable in terms of another, then asks for a third variable "in terms of" one of them. You could chase the algebra symbol by symbol — or you could pick a real number , run the problem forward, and see what falls out. Plugging In (one concrete number) 2. When Plugging In Is Your Best Move PIN isn't a universal shortcut — it earns its keep on a specific shape of problem. Know the signal, and know when to leave it in the toolbox. The problem asks for something "in terms of" a variable, and the choices are themselves algebraic — not a single number. Nested fractions, multiple variables, percent-on-percent changes — anywhere symbolic manipulation invites an error, arithmetic is safer. "Solve for x" with a single numeric answer needs real algebra — plugging in can't verify a unique unknown the same way. If no single number would settle it and you'd need many trials to be sure, plugging in becomes slower than just solving. Four steps, repeated on every PIN problem, in the same order every time. Pick something arithmetic-friendly. Avoid 0 and 1 at first (they can mask errors, since and regardless of the relationship). Common choices: 2, 3, 5, 10, 100. Replace every variable with your chosen number and work the problem using only arithmetic — no symbols.

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