# Chapter 16 Probability Class 11 Maths

In this Chapter, we studied about the axiomatic approach of probability.
The main features of this Chapter are as follows:

Sample space: The set of all possible outcomes
Sample points: Elements of sample space
Event: A subset of the sample space
Impossible event : The empty set
Sure event: The whole sample space

Complementary event or ‘not event’ : The set A′ or S – A

Event A or B: The set A ∪ B
Event A and B: The set A ∩ B
Event A and not B: The set A – B
Mutually exclusive event: A and B are mutually exclusive if A ∩ B = φ
Equally likely outcomes: All outcomes with equal probability
Probability of an event: For a finite sample space with equally likely outcomes
Probability of an event P(A) = \frac{n(A)}{n(S)} , where n(A) = number of elements in the set A,
n(S) = number of elements in the set S.
If A and B are any two events, then
P(A or B) = P(A) + P(B) – P(A and B) equivalently,
P(A ∪ B) = P(A) + P(B) – P(A ∩ B)
If A and B are mutually exclusive, then P(A or B) = P(A) + P(B)
If A is any event, then
P(not A) = 1 – P(A)