Probability

7 years ago

Weightage: 6 – 7 marks

Probability of an event
Types of events
- Elementary events
- Sure Event
- Impossible Event
- Complementary events

Questions based on finding probability of occurrence of events on the basis of given information are asked for 3 – 4 marks.

where we assume that the outcomes of the experiment are equally likely, i.e., all the outcomes occur with equal probability.

Types of events: An event having only one outcome is called an elementary event.
The sum of the probability of all the elementary events of an experiment will always be equal to 1.Lets say we have a bag with 3 balls identical in shape & size having different colours, say red, blue & green.In this case event of pulling out a red ball is an event having only 1 outcome.Similarly, pulling out a green ball or a blue ball also has one outcome. These events will be called elementary events.Now, in this bag if we add 3 identical yellow balls : Y₁, Y₂ & Y₃Then, pulling out a yellow ball will be an event but pulling out Y₁, Y₂ & Y₃ will be elementary event.In both cases you can see that sum of the probabilities of all the elementary events of an experiment is 1.

Sure event: When an event is certain to occur, it is called sure event.
Over here, whenever we put hand in the bag , we will always pull out a ball.Probability of taking out a ball from the bag is 1. Such events are called sure events.

Impossible event: Events which will never occur are called impossible events. For example, in the above given experiment, if we want to take out a black ball, the probability will be zero.The probability of an event can never be negative and it always lies between

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