## Probability of an Event

Probabilities are connected with experiments where the outcome is not well-known in breakthrough or cannot be predicted. Because that example, if you toss a coin, will you attain a head or tail? If you roll a dice will acquire 1, 2, 3, 4, 5 or 6?Probability measures and also quantifies "how likely" one event, concerned these varieties of experiment, will certainly happen. The value of a probability is a number between 0 and also 1 inclusive. An event that cannot happen has a probability (of happening) equal to 0 and the probability of an event that is certain to occur has a probability equal to 1.(see probability scale below). In order to quantify probabilities, we require to define the sample space
of an experiment and also the events that might be associated with that experiment.

## Sample space and Events

The sample space is the set of all feasible outcomes in one experiment.

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Example 1: If a dice is rolled, the sample an are S is provided byS = 1,2,3,4,5,6Example 2: If two coins room tossed, the sample an are S is given byS = HH,HT,TH,TT , wherein H = head and also T = tail.Example 3: If two dice space rolled, the sample an are S is given byS = (1,1),(1,2),(1,3),(1,4),(1,5),(1,6) (2,1),(2,2),(2,3),(2,4),(2,5),(2,6) (3,1),(3,2),(3,3),(3,4),(3,5),(3,6) (4,1),(4,2),(4,3),(4,4),(4,5),(4,6) (5,1),(5,2),(5,3),(5,4),(5,5),(5,6) (6,1),(6,2),(6,3),(6,4),(6,5),(6,6)

We define an event together some details outcome of an experiment. An occasion is a subset that the sample space.Example 4: A dice is rolling (see example 1 over for the sample space). Permit us define event E together the set of feasible outcomes whereby the number top top the face of the dice is even. Event E is provided byE = 2,4,6Example 5: two coins room tossed (see instance 2 above for the sample space). Let us define event E together the set of possible outcomes wherein the number of head obtained is same to two. Occasion E is given byE = (HT),(TH)Example 6: 2 dice room rolled (see instance 3 above for the sample space). Let us specify event E as the collection of feasible outcomes where the sum of the numbers on the deals with of the 2 dice is same to four. Occasion E is provided byE = (1,3),(2,2),(3,1)

## How to calculate Probabilities?

### 1 - classic Probability Formula

It is based on the fact that all outcomes are equally likely.
Total variety of outcomes in E
P(E)= ________________________________________________
Total number of outcomes in the sample space
Example 7: A die is rolled, discover the probability of acquiring a 3.The event of attention is "getting a 3". For this reason E = 3.The sample space S is offered by S = 1,2,3,4,5,6.The number of possible outcomes in E is 1 and also the number of possible outcomes in S is 6. Hence the probability of obtaining a 3 isP(E) = 1 / 6.Example 8: A dice is rolled, uncover the probability of acquiring an also number.The occasion of interest is "getting an also number". For this reason E = 2,4,6, the also numbers on a die.The sample an are S is offered by S = 1,2,3,4,5,6.The number of possible outcomes in E is 3 and the variety of possible outcomes in S is 6. Hence the probability of acquiring an also number isP(E) = 3 / 6 = 1 / 2.

### 2 - Empirical Probability Formula

It provides real data on present cases to determine just how likely outcomes will happen in the future. Let us clarify this utilizing an example30 human being were asked around the colors lock like and here space the results:
 Color frequency red 10 blue 15 green 5
If a person is selected at arbitrarily from the above group the 30, what is the probability that this person likes the red color?Let occasion E be "likes the red color". Hence
 Frequency for red color P(E)= ________________________________________________ Total frequencies in the over table
= 10 / 30 = 1 / 3Example 8: The table below shows students distribution per class in a school.

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 Grade frequency 1 50 2 30 3 40 4 42 5 38 6 50
If a college student is selected at random from this school, what is the probability the this college student is in class 3?Let occasion E be "student from grade 3". Hence
 Frequency because that grade 3 P(E)= _______________________________________ Total frequencies
= 40 / 250 = 0.16

### More References and also links

Probability concerns with Solutions.elementary statistics and also probabilities.