We often come across the term probability. For example - the probability of it raining today is 60% or there is a probability of 90% that the flight will be delayed. Here probability refers to the chance that something will happen.

Probabilities definition

Probability is defined as the measure of the likelihood that a certain event will occur. It is usually expressed as a number between 0 and 1 where 0 indicates no likelihood of the event and 1 indicates certainty that the event will occur.

Probability is given by the formula
Probability of an event occurring = number of times it can happen/ total number of possible outcomes

Examples of probability

Tossing a coin

Take the example of tossing of a coin, the two possible outcomes are heads and tails and in case of a fair coin, there is an equal chance of either outcome. Hence the probability of heads is ½ or 50% and the probability of tails is ½ or 50%.

Throwing a dice
A dice has 6 possible outcomes 1, 2, 3, 4, 5, 6. The probability of any of these outcomes occurring is 1/ 6.

Related terms
Sometimes the following terms are used in relation to probability

Experiment - Experiment is the action where the results are uncertain and will be defined using probability
Sample space - refers to all possible outcomes of an experiment.

Practice questions
Question: There are 20 pebbles in a bag. 5 are brown, 4 are white and the remaining are black. What is the chance that you will pull a brown pebble out of the bag? What is the probability of taking a white pebble out of the bag?
( Answer: Total number of possible outcomes = 20
    Probability of taking a brown pebble out of the bag = 5/ 20 = 25%
    Probability of taking a white pebble out of the bag = 4/ 20 = 20%

Question: There are 52 cards in a deck. What are the chances that you will pull an ace from the deck?
( Answer: Total number of possible outcomes = 52
    Total number of aces = 4
    Probability of pulling an ace = 4/52 = 7.6%

Question: Choose a number between 1 to 5 randomly. What is the probability that the number chosen is even? What is the probability that the number chosen is odd
( Answer:
    Possible outcomes = 1, 2, 3, 4, 5
    Total number of possible outcomes = 5
    Total number of even numbers = 2
    Total number of odd numbers = 3
    Probability of choosing an odd number = ⅗ = 60%
    Probability of choosing an even number = ⅖ = 40%


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