Question:

Find the probability of the events given in Question 2 [ (i) (a) a prime number (b) not a prime number. (ii) (a) a number greater than 5 (b) a number not greater than 5.].

Updated On: Nov 28, 2023
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Solution and Explanation

When a die is thrown, there are total six outcomes, i.e., \(1, 2, 3, 4, 5\) and \(6\)
(i) (a) \(2, 3, 5\) are prime numbers. 
So there are \(3\) outcomes out of \(6\)
Therefore, probability of getting a prime number = \(\frac{3}{6}\) = \(\frac{1}{2}\)


(b) \(1, 4, 6\) are not the prime numbers. 
So there are \(3\) outcomes out of \(6\)
Therefore, probability of getting a prime number = \(\frac{3}{6}\) = \(\frac{1}{2}\)


(ii) (a) Only \(6\) is greater than \(5\)
So there is one outcome out of \(6\)
Therefore, probability of getting a number greater than \(5\) = \(\frac{1}{6}\)
(b) Numbers not greater than \(5\) are \(1, 2, 3, 4\) and \(5\).
 So there are \(5\) outcomes out of \(6\)
Therefore, probability of not getting a number greater than \(5\) = \(\frac{5}{6}\)

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Concepts Used:

Probability

Probability is defined as the extent to which an event is likely to happen. It is measured by the ratio of the favorable outcome to the total number of possible outcomes.

The definitions of some important terms related to probability are given below:

Sample space

The set of possible results or outcomes in a trial is referred to as the sample space. For instance, when we flip a coin, the possible outcomes are heads or tails. On the other hand, when we roll a single die, the possible outcomes are 1, 2, 3, 4, 5, 6.

Sample point

In a sample space, a sample point is one of the possible results. For instance, when using a deck of cards, as an outcome, a sample point would be the ace of spades or the queen of hearts.

Experiment

When the results of a series of actions are always uncertain, this is referred to as a trial or an experiment. For Instance, choosing a card from a deck, tossing a coin, or rolling a die, the results are uncertain.

Event

An event is a single outcome that happens as a result of a trial or experiment. For instance, getting a three on a die or an eight of clubs when selecting a card from a deck are happenings of certain events.

Outcome

A possible outcome of a trial or experiment is referred to as a result of an outcome. For instance, tossing a coin could result in heads or tails. Here the possible outcomes are heads or tails. While the possible outcomes of dice thrown are 1, 2, 3, 4, 5, or 6.