GMAT Probability per Distribution and Equal Likelihoods A bag contains red and blue balls. Exactly half of the balls are red, and the other half are blue. If four balls are removed from the bag, then replaced, what is the Probability that exactly three blue balls will be among those selected? First, let’s figure out … Read More
GMAT Combinatorics: an Introduction Ever wonder why GMAT Permutations and Combinations seem to hard to learn? There’s no good reason–that’s just because they tend to be explained in a terrible way. It’s time for us to fix that! At the risk of blowing all the secrets too early, let’s do this at the beginning. If … Read More
A GMAT Probability Problem with Too Many Moving Parts — How to Deal With a Complex Problem by Isolating its Constituent Parts This problem is so complicated that it’s unlikely to be seen as an actual GMAT Probability question–that is, something you would see in such a complex form on the exam itself–but bear with … Read More
Collapsing Probabilities in GMAT Probability Unsurprisingly, there’s more than one way to look at this phenomenon. Let’s take a look at this straightforward case… Bag 1 contains forty marbles numbered consecutively from 11 to 50. Bag 2 contains fifty marbles numbered consecutively from 41 to 90. If one marble is selected from each bag, what … Read More
GMAT Probability and Number of Distributions x Probability per Distribution The Independent Probability Case for GMAT Probability Now, let’s go back to the example from the previous page, which we can rephrase as this:If a coin is flipped five times, what is the Probability that it will land on Heads only once?That gives us a … Read More
“At Least” Problems in GMAT Probability Hey, remember how all the Probabilities have to be fractions less than one? I mean, after all, it’s reasonably rare for there to be a greater than 100% chance that something will happen. The other thing to bear in mind is that a full Probability–anything that is forgone conclusion–is … Read More
Here’s the Solution to this Crazy-ass Problem: List T Consists of 30 Positive Decimals… Now I’m not going to lie and tell you this question is easy. It’s actually a total beast. And for that reason, I suggest that you repeat this question and repeat it again and then repeat it again until it makes … Read More
CONSISTENTLY ASK YOURSELF: “Am I spinning my wheels?” Remember, that means doing things that won’t get you to the answer any faster. Are you calculating something that won’t yield one of the five answer choices? That’s not to say that the GMAT is giving you wrong information, but rather that the answer choices restrict your … Read More
Here’s a simple GMAT Fractions trick that will help you out when you see a situation where you have to divide by 9 or 99 or 999, etc. It’s actually a really neat little trick and you’ll see it quite often in questions such as this one: Here is a quick tip for you, you … Read More
Arithmetic–or calculation for calculation’s sake–is a waste of time on GMAT Quant Questions. There–I said it. Allow me to add a premise to my argument: insecurity plays a huge role in GMAT Quant Questions. Chew on that for a moment, and let this sink in: Already the human computer is widely displaced by mechanical … Read More