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4 Most Common Types of O Level Probability Questions in the Math Exam

Updated: May 20

Common Types of O Level Probability Questions in the Math Exam

O Level probability topic is an essential topic in the GCE O Level examinations, as part of the E-Math Probability syllabus in Singapore. Understanding and mastering these questions are crucial to score in the O-Level Exam. In this article, we'll break down the four most common types of probability questions students encounter and how to approach them effectively.

The Importance of O Level Probability

The Importance of O Level Probability

O Level Probability questions require students to think critically, analyse situations, and apply mathematical reasoning. This section of the curriculum, developed by the Ministry of Education and guided by the Cambridge Assessment International framework, plays a key role in preparing students for further studies in junior colleges or specialised academic paths. The assessment board emphasises the importance of this topic due to its everyday applications.

Key Objectives

  1. Fundamentals Mastery: Understanding fundamental concepts of probability.

  2. Analytical Skills: Applying logical thinking to solve probability problems.

  3. Graphical Interpretation: Interpreting probability visually through diagrams.

Let's dive into the four most common types of probability questions O Level students are likely to face.

Below are the 4 most common types of probability questions in the O-Level exam:

1. Probability of Single Events

These questions challenge students to find the probability of a single event occurring under specific conditions. For example, determining the probability of rolling a specific number on a six-sided die or drawing an Ace from a deck of cards.

An example is finding the probability of rolling a specific number on a fair six-sided die. 

2. Probability of Simple Combined Events

Combined events involve calculating the probability of events happening in succession or simultaneously. Understanding concepts like independence and dependence is crucial for solving these questions effectively.

Questions might include finding the probability of multiple events occurring in a sequence or simultaneously. This often involves grasping concepts such as event independence and dependence. Various methods are available for representing the sample space, with two notable examples being possibility diagrams and tree diagrams.

Sample Space Representation

Two common methods for representing the sample space of combined events include:

Possibility Diagrams

Possibility diagrams represent outcomes as points on a grid or in a table based on context. They are effective for two events with numerous possible outcomes. For instance, calculating the sum of numbers from rolling two dice can be represented on a diagram.

An example of a possibility diagram which shows the sum of the two numbers:

Probability of Single Events

Tree Diagrams

Tree diagrams represent outcomes at the branches and their probabilities on the branches. They are ideal for scenarios involving multiple events with fewer outcomes.

An example of a tree diagram:

Tree Diagrams


A tree diagram can represent the probability of drawing two cards from a deck without replacement. The first branch shows the probabilities of the initial draw, and subsequent branches show the changing probabilities based on earlier draws.

Complementary Events

3. Complementary Events

Complementary events involve finding the probability of an event or its complement. For instance, if a problem asks for the probability of a non-Indian student being chosen, students can subtract the probability of an Indian student being chosen from 1.


If the probability of a student owning a smartphone is 0.7, the complementary probability of a student not owning a smartphone is:

Probability of Not Owning a Smartphone=1−0.7=0.3

Probability of Not Owning a Smartphone=1−0.7=0.3

4. Conditional Probability

Conditional probability involves finding the probability of an event given that another event has already occurred. This is crucial in problems where an event influences subsequent outcomes.


In a deck of cards, the probability of drawing a second red card given that the first card drawn was red is calculated by considering the reduced deck and removing one red card from the count.

Complementary Events

O Level Probability topic encompasses critical mathematical skills that extend beyond exams. Understanding probability questions in O-Level not only aids students in excelling in the O-Level exams but also provides valuable analytical tools for practical applications. By mastering the four most common types of questions discussed above, secondary school students, whether attending public schools or preparing as private candidates, can ensure their success in the Singapore-Cambridge GCE exams.

For parents seeking to equip their children with the essential skills and knowledge to excel in O Level Probability and beyond, enrolling them in AGrader Learning Centre's Secondary Maths Tuition is the prudent choice.

Understanding O Level Probability extends beyond exam success; it cultivates critical analytical skills with practical applications. AGrader's meticulously planned lessons, aligned with the latest MOE syllabus, ensure students receive relevant and comprehensive instruction. Taught ahead of school, these lessons provide a crucial edge in grasping complex concepts.

With high-quality worksheets complementing each lesson, students gain invaluable practice and reinforcement. What's more, the inclusion of EverLoop Modules, offered at no extra cost, further enhances learning. These modules provide exam-focused practice, enabling students to master key concepts and excel in the O-Level exams.

Don't let your child miss out on the opportunity to thrive academically and develop essential analytical skills. Enrol them in AGrader Learning Centre's Secondary Maths Tuition today.

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