What is Probability? | Class 9 Mathematics Notes

7.1 WHAT IS PROBABILITY?

Probability is a mathematical measure used to express the likelihood or chance that a particular event will occur. Unlike physical measurements such as length, area, or volume, probability quantifies uncertainty and randomness in events. Everyday questions such as "Is it going to rain today?", "Will our school win the hockey match tomorrow?", or "Will I be chosen in the lucky draw?" are examples of events involving chance. These are called random events because although we know the possible outcomes, we cannot predict with certainty which outcome will happen. For example, it may rain or not rain today; the school hockey team may win, lose, or draw; and any student’s name may be drawn in the lucky draw. The uncertainty arises because of the element of chance or randomness involved.

People often express their belief about the likelihood of an event using terms like impossible, certain, less likely, more likely, or equally likely. These expressions are subjective and based on personal interpretation of evidence, such as weather conditions or past experiences. For instance, one friend may say it is unlikely to rain because the sun is shining, while another may think rain is possible because it is hot and humid. This is called subjective probability, reflecting personal judgment rather than objective measurement.

Probability deals with uncertainty and chance, which are common in real life. As society becomes more complex, many questions have multiple possible answers rather than fixed ones. Therefore, learning how to estimate probability objectively, based on evidence rather than opinion, is important. This chapter introduces the concept of randomness, the probability scale, and methods to measure probability objectively.

📊 Diagram: Figure shows examples of random events: a coin toss with possible outcomes heads or tails; a die roll with outcomes 1 to 6; and a lucky draw where one slip is randomly selected from many.

🧪 Activity: Think and Reflect: Why is the coin toss considered a fair method to decide which cricket team bats first? Discuss the role of unpredictability in fairness.

🔗 Connection: This section introduces the concept of randomness, leading to the next subsection which defines randomness more precisely and explains its role in probability.