4 - 760+: Finding Patterns in PS Questions When You Don’t Immediately See Them

By richc On Oct 21, 2021 In  Quant Verbal IR Study Plans General GMAT MBA Advice & Tips 

Since the GMAT is a standardized Test, all of the questions that you’ll face are designed around one or more patterns. Sometimes the patterns are obvious – such as math formulas or grammar rules. Sometimes the patterns are more subtle - such as number properties or causality arguments.
With the proper study materials and Study Plan, you can learn all of the necessary patterns and train to properly use them. However, sometimes the patterns are so rare that they’re not worth learning in advance and sometimes they are essentially ‘hidden’, meaning that you won’t immediately see the pattern involved. However, the pattern is still there – and correctly answering some of the tougher questions on the GMAT will be considerably easier IF you are comfortable with the idea that you can ‘play around’ with the prompt a bit and define what the pattern is.
“Playing around” with a GMAT question is essentially about running little ‘experiments’ on it. In basic terms, you need to ask “what if….?” and then go about determining the result.
For example, here is a question from the PS Forums here. Your immediate task is NOT to calculate the result – it’s to figure out the first 4 terms in the sequence and THEN deduce a pattern within those 4 terms….
For every integer K from 1 to 10, inclusive, the Kth term of a certain sequence is given by:
[(-1)^(K+1)] x [1/(2^K)].
If T is the sum of the first 10 terms in the sequence, then T is….
A. Greater than 2
B. Between 1 and 2
C. Between ½ and 1
D. Between ¼ and ½
E. Less than ¼
So… what have you deduced? The answer appears below:
The first four terms are: +1/2, - ¼, + 1/8, - 1/16. Thus, the terms ‘flip-flop’ between positive and negative. In addition, each negative term, when ‘paired’ with the positive term immediately ahead of it, cuts the positive term in half…
+1/2 – ¼ = +¼
+1/8 – 1/16 = +1/16
Now that you recognize this pattern, you should be able to quickly determine that the value of the other three ‘pairs’ gets progressively smaller: 1/64, 1/256, 1/1024
The question asks for the sum of those first 10 terms, but doesn’t provide exact answers – it provides RANGES, so you do NOT have to be exact with your math. What are we really adding to +1/4? A bunch of increasingly shrinking (and significantly small) fractions. Thus, the sum has to be….
A little more than ¼. Final Answer: D
In the next post, I’ll list a few additional PS prompts for you to ‘play around’ with. Remember the immediate goal – decipher the pattern first. Then, use whatever pattern you discover to answer the question.
GMAT assassins aren’t born, they’re made,
If you have any questions about anything in this thread, then you can feel free to contact me directly via email (at [email protected])

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