Probability for CAT is an important topic in the CAT quantitative aptitude section. You can expect 23 questions from probability in the quant section in CAT. Probability helps us determine the odds of an event happening or not happening.
Probability is simply how likely something is to happen. Whenever you’re not certain about the outcome of an event, you can talk about the probabilities of certain outcomes—how likely they are. Probability can range from 0 to 1, where 0 means the event to be an impossible one and 1 indicates a certain event.
For example, when we toss a coin, either we get Head OR Tail, only two possible outcomes are possible (H, T). But when two coins are tossed then there will be four possible outcomes, i.e {(H, H), (H, T), (T, H), (T, T)}.
The probability formula is defined as the possibility of an event to happen is equal to the ratio of the number of favourable outcomes and the total number of outcomes.
Probability of event to happen P(E) = Number of favourable outcomes/Total Number of outcomes
Term  Definition  Example 
Sample Space  The set of all the possible outcomes to occur in any trial  1. Tossing a coin, Sample Space (S) = {H,T} 2. Rolling a die, Sample Space (S) = {1,2,3,4,5,6} 
Sample Point  It is one of the possible results  In a deck of Cards:

Experiment or Trial  A series of actions where the outcomes are always uncertain.  The tossing of a coin, Selecting a card from a deck of cards, throwing a dice. 
Event  It is a single outcome of an experiment.  Getting a Heads while tossing a coin is an event. 
Outcome  Possible result of a trial/experiment  T (tail) is a possible outcome when a coin is tossed. 
Complimentary event  The nonhappening events. The complement of an event A is the event, not A (or A’)  In a standard 52card deck, A = Draw a heart, then A’ = Don’t draw a heart 
Impossible Event  The event cannot happen  In tossing a coin, impossible to get both head and tail at the same time 
Usually you would encounter two major types of problems in Probability with the the use of
conjunctions AND and OR.
In general, event definition means breaking up the event to the most basic building blocks, which are commonly through the two English conjunctions— AND and OR.
Here:
A’ = S – A.
Event A and A’ are mutually exclusive and exhaustive.
Consider the example of tossing a coin. Let P(E) denote the probability of getting a tail when a coin is tossed. Then,
When two events, A and B, are independent, the probability of both occurring is:
P(A and B) = P(A ∩ B) = P(A) × P(B)
218 videos139 docs151 tests

1. What is the concept of conditional probability? 
2. How does Bayes' Theorem relate to probability? 
3. What are mutually exclusive events in probability? 
4. What are equally likely events in probability? 
5. What is meant by an exhaustive set of events in probability? 

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