GMAT® Quant: The 'Use What They Give You' Principle
If you've ever spent two minutes on a GMAT® quant problem doing hard algebra, only to realize there was a much simpler path — you've felt the gap between knowing the math and knowing how to approach the problem.
That gap is what this article is about.
On GMAT® quant questions, you're almost never given information unless it's necessary for solving the problem. But in practice, a lot of us end up ignoring half of what the problem hands us — and then reaching for a harder method than we need.
We walked through three problems in Episode 30 of Real GMAT® Problems, our podcast series. Each one demonstrates a different version of the same principle: use what they give you, pick the right method, and estimate when the problem invites you to.
Principle 1: Use the Formula They Describe
When a problem describes rates and times, the Rate × Time = Work formula is almost always the path. The problem tells you the relationship — your job is to organize it.
This is the combined work rate problem: one machine takes 4 hours, another takes 3 hours, how long do they take together? The problem says "working simultaneously at their respective constant rates" — that's the cue to find individual rates and add them.
The full walkthrough is here: "It Would Take One Machine 4 Hours to Complete a Large Production Order..." — GMAT® Worked Solution. This problem was also covered in Episode 44 of our podcast series.
The key insight: the problem gives you the time each machine takes. It doesn't give you the rates directly. But Rate × Time = Work lets you derive the rates, combine them, and then find the combined time. The formula is the bridge between what you're given and what you're asked.
Principle 2: When Answers Have Variables, Plug In Numbers
When a problem gives you variables in the answer choices, you have a choice: do algebra with the variables, or replace them with numbers.
Both methods work. The question is which one produces fewer errors for you personally.
For most people — especially those who don't feel confident with algebraic manipulation — plugging in numbers is the more reliable path. You replace each variable with a simple number, compute an answer with arithmetic, then plug those same numbers into each answer choice to find the match.
The advantage: you're doing basic arithmetic instead of manipulating equations. Adding, subtracting, and comparing integers is where most people make fewer mistakes than distributing variables and combining like terms.
We walk through both methods — algebra and plugging in numbers — side by side in this worked solution: "To Mail a Package, the Rate Is x Cents for the First Pound..." — GMAT® Worked Solution
If you're already comfortable with algebra and getting consistent results, keep doing what works. But if you find yourself getting lost in the variables — or if you want a method that's more error-tolerant — try plugging in numbers on your next few variable-answer problems and compare your accuracy.
Principle 3: When a Problem Says "Approximately," Estimate
When a problem includes the word "approximately" or "closest to," that's an invitation to estimate. Taking that invitation is usually the difference between a 30-second solution and a 3-minute slog.
The compound interest problem from Episode 30 is the clearest example. The problem gives you a rule: at R% interest, money doubles in approximately 70/R years. It then asks for the value of a $5,000 investment at 8% interest after 18 years.
Two paths:
Path A: Use the compound interest formula. Calculate . Without a calculator, taking something to the 18th power is rough.
Path B: Use the rule they gave you. years to double. 18 years is two doubling periods. $5,000 → $10,000 → $20,000. Answer: (A).
Path B takes about 20 seconds. Path A takes several minutes and is error-prone without a calculator.
The problem told you to estimate. The rule was sitting right there. Using it isn't a shortcut — it's the intended solution.
The Common Thread
All three principles come from the same place: pay attention to what the problem gives you.
- A problem mentions rates and times? Use Rate × Time = Work.
- A problem has variables in the answers? Plug in numbers.
- A problem says "approximately" and gives you a rule? Estimate.
None of these require flashcards or memorization. They require reading the problem carefully and responding to the signals it's sending.
The GMAT® quant section is designed to reward reasoning over calculation speed. The problems reward test takers who notice the signals and use the tools they're given. When you find yourself doing hard math on a GMAT® problem, pause and ask: did the problem give me something I'm not using?
Common Mistakes
Ignoring the given formula and reaching for a harder one
On the compound interest problem, a significant percentage of test takers go straight to the compound interest formula — which requires calculating an 18th power without a calculator. The problem gave them a simpler rule. They ignored it.
Doing algebra when plugging in numbers would work
On the mailing package problem, wrong answers are spread across all four incorrect options. There's no single trap — people are just getting lost in the algebra. Plugging in numbers converts the algebra into arithmetic, which is easier to execute correctly.
Calculating exactly when the problem says "approximately"
When a problem says "approximately," the answer choices are usually far enough apart that a rough estimate lands you on the right one. Calculating the exact value wastes time and introduces unnecessary error opportunities.
Forgetting to check what you're solving for
On the rates problem, about 14% of test takers solve for the combined rate (7/12) when the question asks for the combined time (12/7). The math is correct. The quantity is wrong. Writing what's asked and given before starting the math prevents this.
Study Action Items
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On your next 10 quant problems, before you start calculating, ask: what did this problem give you, and what is it asking for? Write both down.
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Try plugging in numbers on your next 3 variable-answer problems. Compare your accuracy to your usual algebra approach.
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When a problem says "approximately" or "closest to," commit to estimation. Don't calculate the exact value unless the answer choices are too close together for estimation to work.
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After each problem, reflect: did you use everything the problem gave you? If there's unused information, was it truly unnecessary, or did you miss a signal?
FAQ
What does "use what they give you" mean on the GMAT® quant section?
On GMAT® quant questions, information given in the problem statement is almost always necessary for solving. If a problem mentions a formula, a rule, or a relationship, that's usually the intended path. Ignoring given information and reaching for a harder method wastes time and introduces errors.
Should I plug in numbers or do algebra on GMAT® quant problems?
When answer choices contain variables, plugging in numbers is usually the more error-tolerant method. You replace variables with simple numbers, compute an answer, then match it against the answer choices. Algebra works too — but if you're prone to manipulation errors, plugging in numbers reduces the number of things that can go wrong.
When should I estimate on GMAT® quant problems?
Estimate when the problem says "approximately," "closest to," or when the answer choices are far apart. Don't estimate when the answer choices are 1 apart — the GMAT® designs some problems to reward estimation and others to punish it. The answer choices tell you which kind you're looking at.
How do I know which formula to use on a GMAT® quant problem?
Look at what the problem describes. If it mentions rates and times, use Rate × Time = Work (or Rate × Time = Distance). If it mentions percents, convert to fractions for cleaner computation. If it gives you a specific rule — like the 70/R doubling rule for compound interest — use that rule instead of the general formula.
How does this connect to the rate chart system from Episode 44?
The rate chart from Episode 44 of our podcast series is the organizational application of "use what they give you." The chart captures the given information (rates, times, work) in a structured format. This article covers the broader principle — recognizing signals across different problem types, not just work rate problems.
Want to Learn Even More?
Listen to Episode 30 of Real GMAT® Problems for the full audio walkthrough of all three problems, including Isaac's commentary on when to estimate, when to plug in numbers, and why so many test takers ignore the tools the problem hands them.
For related strategy, read:
- GMAT® Work/Rate Problems: Why Organization Matters — the rate chart system from Episode 44
- Testing Numbers on the GMAT®: A Simple System That Beats Memorizing Number Theory — the number-testing system from Episode 38 of our podcast series
- GMAT® Average Speed Problems: The Rate Chart and the Formula That Solve Them — distance and speed applications from Episode 47 of our podcast series
Worked solutions for this episode:
- Problem 1: "It Would Take One Machine 4 Hours to Complete a Large Production Order..." — combined work rates (from Episode 44)
- Problem 2: "To Mail a Package, the Rate Is x Cents for the First Pound..." — algebra vs plugging in numbers