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Probability
Tutorial on Probability
Class 9
What is probability
• Probability is the measure of the likeliness that
an event will occur. Probability is quantified as a
number between 0 and 1 (where 0 indicates
impossibility and 1 indicates certainty)
• It is widely used in the study of Mathematics,
Statistics, Gambling, Physical sciences, Biological
sciences, Weather forecasting, Finance etc. to
draw conclusions. Insurance companies uses this
to decide on financial policies
Terms in Probability
Randomness
In mathematics, When next outcome of the
experiment can not be determined then we say
it is a random experiment e.g. Consider the
dice. When we throw the dice, we cannot
determine what number will come Since we
cannot predict the next outcome, we may say it
is a random experiment
Trial
A trial is an action which results in one or
several outcomes, for example each toss of the
coin and each throw of the die are called trials
Terms in Probability
Independent Trial
Successive trials of some random event for
example tosses of a coin, throws of a die are
said to be independent if the outcome of any
one trial does not impact the outcomes of any
others.
Experiment
Experiment and trial are same thing as such.
An experiment is a situation involving chance
or probability that leads to results called
outcomes. But sometimes we use experiment to
refer to whole large number of trials.
Terms in Probability
Event
An event is a possible outcome of the
Experiment. Like head coming in a toss
Sample space
It is a set of all possible outcomes of an
experiment.
e.g. when we coin is tossed, the possible
outcome are Head and Tail. So sample space is
Head and tail
Empirical Probability
1) Experimental or empirical probability is an
estimate that an event will happen based on how
often the event occurs after performing an
experiment in a large number of trials.
2) It is a probability of event which is calculated
based on experiments
3) Empirical probability depends on experiment and
different will get different values based on the
experiment
Empirical Probability
1) If the event A, B, C covers the entire possible
outcome in the experiment. Then,
P (A) +P (B) +P(C) =1
2) The probability of an event (U) which is
impossible to occur is 0. Such an event is called an
impossible event
P (U)=0
3) The probability of an event (X) which is sure (or
certain) to occur is 1. Such an event is called a sure
event or a certain event
P(X) =1
4) Probability of any event can be as
0≤ P(E) ≤1
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