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鈥檝e noticed over the years is it鈥檚 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

## Magoosh Brain Twister: Flipping Out – Explanation

Make sure you remember this week’s question before moving on to the explanation. Question If a fair coin is tossed six times, what is the probability of getting exactly three heads in a row? (A) 1/16 (B) 3/16 (C) 1/8 (D) 3/8 (E) 1/2 Answer and Explanation A good way to think about […]

## Magoosh Brain Twister: Flipping Out

Welcome back, brave Magooshers! Best of luck with this week’s diabolical GRE Brain Twister. 馃檪 If a fair coin is tossed six times, what is the probability of getting exactly three heads in a row? (A) 1/16 (B) 3/16 (C) 1/8 (C) 3/8 (D) 1/2 See you on Thursday for the answer and […]

## 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鈥檚 easy to say order doesn鈥檛 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. […]

## “Chelsea – it’s time for a Kindle” Challenge Question

Try the question below. It is not as tough as some of the challenge questions on this blog. That said, see if you can solve in less than 1 minute. Good luck! 馃檪 Chelsea has a bookshelf consisting of ten classics: four Russian novels, three British novels, two French novels, and a German novel. If […]

## GRE Multiple Answer Challenge Question: Astronauts

In most likelihood, you will only get one or two combinations/permutations questions per test. Typically, the questions are quite challenging. Knowing the standard formulas won’t be enough; you’ll also have to use logic, and a fair amount of grit. Below is a question that will really force you to think, and rely on that grit. […]

## 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鈥檝e […]

## 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 […]

## GRE Counting and Probability: Practice Question of the Week #39

Here’s this week’s practice question– good luck, we’ll be posting the answer tomorrow! How many integers between and 聽are such that the sum of their digits is ? 190 210 211 230 231 Update: Answer/explanation post!

## GRE Permutations: Practice Question of the Week #37 Answer

Here’s the answer to yesterday’s practice question, thanks for sending in all of your answers! Video Explanation