Question:

What is the probability of 53 Fridays in an ordinary year?

Updated On: Aug 16, 2023
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Solution and Explanation

To determine the probability of having 53 Fridays in an ordinary year, we need to consider the possible combinations of days of the week for each month and take into account leap years.
In an ordinary year, there are 365 days. This means that there will be 52 complete weeks of 7 days each, which gives us 364 days. The remaining day can fall on any day of the week.
Since 7 does not divide evenly into 365, there will be one day left over. Therefore, there are two possibilities: either there will be 52 Fridays (with the remaining day falling on a different day of the week), or there will be 53 Fridays (with the remaining day falling on a Friday).
Hence, the probability of having 53 Fridays in an ordinary year is 1/7, or approximately 0.1429 (14.29%).
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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.