• 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.