Probability questions are one of the most hated kind of questions on the GMAT. After all, the "probability" of getting the answer right (if you are a Poet) is pretty low. Although, under timed conditions, many Quants struggle to get it right too.
First of all, you don't need to worry too much about any one topic on the GMAT. It's just not worth the hassle to fret over something that might not even show up on test day! Still, if you want to get Probability questions right, I am going to give you some very basic tips that will at least help you narrow down the answer choices and eliminate the wrong ones.
So what is probability? Its the mathematical representation of "chance".
Basically, if I gave you a coin and told you to toss it just once, you will either get heads or tails. So, if I ask, what are the chances of getting heads, you might say 50%. How did we calculate that? Simple.
Number of total possible outcomes: 2 (Heads or Tails)
Number of favorable outcomes: 1 (Heads)
Simple divide number of favorable outcomes by number of total outcomes, or
Number of favorable outcomes = Probability
Number of Total possible outcomes
1 = 0.5 Multiply this by 100 to get probability in percentage, i.e. 0.5 x 100 = 50%
2
Now, what if you don't have the time or don't really need to calculate probability?
How do you guesstimate?
Golden Rule: Always calculate the total number of outcomes first! That's it!
If you have the denominator, you will be able to eliminate a couple of choices in most questions.
After that you may or may not be able to calculate the number of favorable outcomes, but you would be able to guess better.
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