Do you know the difference between permutation and combination? No? You’re not alone. Combinations and permutations are the bane of many students. Yet, what I’ve noticed over the years is it’s not so much both of them that are the issue as it is which one to use for a particular problem: the combination vs […]

# Archive | Combinations and Permutations

## Does Order Matter? Combinations vs. the Fundamental Counting Principle on the GRE

When trying to decide whether to use the combination formula, many students have trouble applying the “does order matter” test–deciding if outcomes differ. It’s easy to say order doesn’t matter when it in fact does, and vice versa. Once you get it, it’s really useful, but it can take a bit of thinking and re-thinking. […]

## GRE Math Multi-subject Challenge Question

Once in a while it is fun to take a concept in an official GRE question and run with it. The question below is inspired by a question from the 2nd edition Official Guide. That is not to say it is that similar; I have only extracted a couple of concepts from that problem. I’ve […]

## Breakdown of the Most Commonly Tested GRE Quant Concepts

The 2nd edition Official Guide has just been released. At the back of the book is a new test (GRE Practice Test 2). In general, the concept break down is not surprising, if you look at the concepts that pop up in Practice Test 1 (which is the same as the practice test in the […]

## The Difficulty of Context: Combinations and Permutations Questions

Over the last couple of months, I have covered a fair amount of GRE combinations and permutations questions on the blog. I’ve gone from the very basic to the very difficult (so difficult that they are more ‘fun problem’ than practical practice). Often, when you are stumped on a problem, it is not that the […]

## Three GRE Challenge Combinations and Permutations Problems

These challenge questions are great for extra practice. However, be warned: while I provide the answers, I don’t provide the explanations. If you’d like to try practice problems with explanations, check out my biweekly Brain Twisters! Over the last few weeks, I have gone through GRE combinations and permutations. My goal is to make this […]

## Combinations and Permutations Practice Questions and Video Explanations

As a continuation of my introduction to Combinations and Permutations, here are some practice problems to test the strategies I demonstrated. Also, I am trying out a new format. Instead of giving you practice problems and then writing out a half-page description for each one, I am simply going to give you the questions. But don’t […]

## GRE Combinations and…Non-combinations

Whenever I see a GRE resource label its counting section as “Combinations and Permutations,” a small part of me dies a little. Okay, that’s an exaggeration, but I am concerned about the misleading message that this sort of title conveys. To me, it suggests that counting questions can be solved using either permutations or combinations, […]

## Prime Numbers and Probability – GRE Math Problem

Oftentimes, math problems will require that you know more than one concept. Sometimes, you’ll have to know the difference between an integer and a number in order to get the question right. Below, I’ve combined prime numbers with probability, two subjects already covered in this blog. The question below isn’t easy and actually takes a […]

## Revised GRE Math Question Re-spin — The Best Way to Get Ready for the New GRE!

Try this question out and see how you do. Which of the following is NOT a factor of ? 17 21 25 29 42 51 85 121 Factorials can be intimidating. First off, it’s very difficult to calculate factorials over 6, much less find the factors. However, when finding the factors of a factorial, we […]