As a GMAT 99th percentile instructor, I want to share a crucial insight into how you can achieve "super quick solutions" on GMAT Quantitative questions. We'll focus on Arithmetic Progression (AP), which I consider the "most commonly asked sequence on GMAT".
Don't Miss the Clues: Identifying Arithmetic Progression
Many GMAT quant questions can be solved incredibly fast if you know how to identify the underlying concept. What might appear on the surface as "just an averages or a statistics-based question" can transform into a swift solve by combining it with the power of sequences.
The key is to look for specific clues. In my experience, the most important one is a particular type of phrasing hidden in plain sight. Click on the sentence below to see if you can spot the phrase that instantly signals an Arithmetic Progression.
"The average of n consecutive multiples of three is 27..."
(Click to identify the key phrase)
The moment you see "consecutive multiples," you should immediately recognize that you're dealing with an Arithmetic Progression. Why? Because in such a sequence, "each subsequent term is three more than the next", which is the defining characteristic of an AP: a constant difference between terms. My goal is always to equip you with methods that lead to "very very quick solutions," and recognizing this connection is paramount.
Don't Miss the Clues: Identifying Arithmetic Progression
1. Average is Middle Term
In an AP with an odd number of terms, the average is simply the middle value. This is highly intuitive and a fast way to find the average.
2. Average of First & Last
The average of any AP is always the average of its first and last terms. This is a game-changer when you don't know the number of terms ('n').
Putting It to the Test: An Interactive Data Sufficiency Example
Question: What is the least value of a sequence of 'n' consecutive multiples of three with an average of 27?
Statement (1)
The highest value is 36.
Statement (2)
The range is 18.
Since each statement is sufficient independently, the answer is (D).
Beyond AP: The World of GMAT Sequences
While Arithmetic Progression is a common focus, it's important to remember that there are six main types of sequences tested on the GMAT. Mastering the identification and properties of each will significantly enhance your Quant score. I've covered all six types in other resources, which you can find on our website if you're looking to deepen your understanding further.
My aim is to simplify the GMAT journey for you. By understanding these key identification clues and applying the core properties of AP, you'll be well on your way to acing those quantitative questions. Keep practicing, and keep an eye out for those subtle but powerful clues!