- Probability means the chance of occurrence of an event.
- Event means occurrence of something.
- The events that occur purely due to chance are grouped into two main categories on the basis of their relationships with each other.
i) Mutually exclusive events (MEE):
- The occurrence of one event prevents the occurrence of other.
- Eg: tossing of coin, rolling a dice.
- Probability of MEE is, P= 1/n, where n is no. of events.
- So, the probability of getting head in tossing of a coin once = ½ = 0.5.
- The occurrence of any one of the two or more MEE can be calculated by using P = 1/n + ……+ 1/n formula.
ii) Independent events:
- An independent event is an event that has no connection to another event’s chances of happening (or not happening).
- In other words, the event has no effect on the probability of another event occurring.
- When two events are independent, one event does not influence the probability of another event.
- Eg: two coins, A and B are tossed together , the P of getting HH= ½ x ½. , TT= ½ x 1/2 , HT = ½ x ½
- Formula: (a+b)2, where a= P of head (one event) and b= P of tail (Another event). If four coins are tossed: P = (a+b)4.
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