Strategies, Sample Questions, and Random Ramblings.

by ejkiv

July 19, 2015

The reason that we covered combinations and permutations before GMAT probability is that the more difficult probability problems will use these concepts. Probability measures the likelihood that something will happen and will be measured in fractions or decimals. This is always expressed with a number that is between 0 and 1 inclusive. The foundation of probability comes from this equation:

If you flip a coin, the probability of getting heads is .5 because there is one outcome out of 2 possible.

The more difficult probability questions will undoubtedly have you do some more operations. The first of these to be aware of is the probability of two independent events happening. Because their probabilities do not affect each other, they are multiplied together to arrive at your answer.

If Team A has a 60% chance of winning their game and there is a 30% chance of rain, what is the probability that Team A wins while it is raining?

You will notice that this is signified by the word “and” much like when we saw and in combined combination problems (“both” is another good indicator to multiply probabilities).

The next word on the hit list is “or.” It is this word that makes people struggle so much with probability. The reason is that it can signify any number of operations. All of these examples are a bit different:

If Team A has a 60% chance of winning their game and there is a 30% chance of rain, what is the probability that Team A wins or it rains?

If there are 20 marbles in a bag and 20 are red and 8 are blue, what is the probability that you pick a red or blue marble?

Greg R., client, New York City

Emil C., client, Singapore

Chris S, client, New York City