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1. Define (a) random experiment, (b) sample space, (c) simple event, and (d) compound event.
(a) An experiment or activity whose outcome (result) is not predictable before hand is called a
random experiment. Eg. Tossing a fair coin
(b) Sample space is the set of all possible outcomes of a random experiment. It is denoted by S.
In case of a coin toss, S = {H, T}
(c) A simple event is any individual outcome of a random experiment. For a coin toss, A = {H} is a
simple event.
(d) A combination of two or more simple events is a compound event. For a coin toss, B = {H or T}
is a compound event.
2. What are the three approaches to determining probability? Explain the differences among them.
The three approaches to determining probability are:
(a) Classical Approach
:
Classical probability rests on the assumption that all the outcomes of an experiment are equally
likely. The classical probability makes use of rules and laws. It involves conducting experimental
trials.
P(A) = Number of outcomes favorable to A / Total number of possible outcomes
Thus, we can adopt the classical approach only when the events are equally likely, mutually
exclusive and exhaustive.
(b) Relative Frequency Approach
:
Relative probability is based on historical data. In this method
P(A) = Number of times the event A occurred in the past/ Total number of chances there were for A
to occur
This approach is not based on rules or laws but on what has happened in the past.
(c) Subjective Approach
:
The subjective probability is based on personal judgment, knowledge, experience and intuition. For
example doctors sometimes assign subjective probabilities to life expectancy for people diagnosed
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 Spring '11
 acc101

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