What This Episode Covers
Three real GMAT® average speed problems from the 11th edition of the Official Guide for GMAT® Review, increasing in difficulty. Isaac introduces two tools that handle almost every distance and speed question on the GMAT®: the rate chart and the average speed formula (total distance over total time).
The episode also covers a pattern that trips up a lot of test takers — the temptation to simply average two individual speeds. Isaac explains why that almost never works and what to do instead.
Problems Covered
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Car X and Car Y traveled the same 80-mile route — A warm-up that introduces the rate chart and the average speed formula. Straightforward setup, one equation, one unknown. Read the worked solution →
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Jill went up a hill at an unknown constant speed — The difficulty jumps. Two unknowns, "along the same route" as a key phrase, and an average speed given for the whole trip. This is where the rate chart starts to earn its keep. Read the worked solution →
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During a trip on an expressway, Don drove X miles — The hardest of the three. A rate chart with four rows, algebra with two variables that cancel, and a percent change layer on top. Isaac talks through the "leaps of faith" needed when the path forward is not obvious. Read the worked solution →
Key Takeaways
Average speed = total distance / total time. Write it out every time. The single most common mistake on average speed problems is averaging the individual speeds from each leg of the trip. That almost never works because the traveler spends different amounts of time at each speed. Writing the formula at the top of the problem is a cheap and effective defense against this pitfall.
The rate chart organizes what you know and reveals what you can solve for. Rate × Time = Distance across the top. One row per leg of the journey, plus a total row when you have an average speed. Fill in what the problem gives you, then solve for the gaps. It keeps moving parts visible.
"Along the same route" means the distances are equal. You may not know the actual number, but you can use the same variable for both. That phrase appears frequently in average speed problems and it is the key to setting up the algebra.
Leaps of faith are part of problem-solving. You will not always see five steps ahead. If the chart is organized and the formula is written, you have enough reason to proceed. Try solving for what you can and see what simplifies. Variables may cancel. Fractions may reduce. Sometimes the path only becomes clear after you take the next step.
The rate chart may feel like overkill on easy problems. Use it anyway. The habit pays off on harder problems where organization is the difference between getting stuck and finding the answer.
Percent change has a formula too. (New − Old) / Old × 100. When the problem says "percent greater than," the value after "than" is the old value. Write that down and it removes the guesswork.
Related Reading
- GMAT® Average Speed Problems: The Rate Chart and the Formula That Solve Them — the strategy article covering all three problems
- Car X and Car Y Traveled the Same 80-Mile Route — GMAT® Worked Solution
- Jill Went Up a Hill at an Unknown Constant Speed — GMAT® Worked Solution
- During a Trip on an Expressway, Don Drove X Miles — GMAT® Worked Solution