Interval in Math – Meaning, Definition, Examples

Welcome, math explorers! At Brighterly, we believe in illuminating the path of mathematical discovery for children. Today, we’re setting off on a journey to understand the concept of “interval” in mathematics. This might seem like a complex term at first, but don’t worry! We’re here to break it down, making it simpler and brighter, just as the name Brighterly implies.

An interval in math is, in essence, a way of expressing a range of numbers. Think about going on a treasure hunt: you know that the treasure lies somewhere between point A and point B. That ‘somewhere’ is essentially what we mean when we talk about intervals. Just as in our treasure hunt, an interval contains all the “points” or numbers between two given numbers.

For example, if we talk about an interval between 3 and 5, it will include numbers like 3.1, 4.5, 4.999, and every possible number you can think of between 3 and 5! Intervals are like the secret bridges in the kingdom of mathematics, connecting different points on the number line and opening up a path for us to understand more complex concepts like continuity, functions, and calculus.

Interval in Math

An interval in math is a set of real numbers that contains all numbers between any two numbers in the set. For example, if you have the numbers 3 and 5 in your set, all the real numbers between 3 and 5 are also included in the set. This means that 4, 3.5, 4.5, and even numbers like 3.789 are included! Intervals are an important part of mathematics and can be found in various branches such as calculus, algebra, and statistics.

What is an Interval in Math?

In math, an interval can be thought of as a ‘stretch’ of the number line. It’s the building block for the idea of continuity in calculus, a crucial concept that helps us understand change and motion. In simpler terms, if you imagine a number line, an interval is a segment of that line that includes all the numbers between two given points. Whether those endpoints are included or excluded, depends on the type of interval.

What is Interval Notation?

Interval notation is a method used in mathematics to specify and simplify the way we represent these intervals. Instead of writing out all the numbers, interval notation uses parentheses and brackets to show which numbers are included in the set. Parentheses, ( ), are used to indicate that the endpoints are not included, while brackets, [ ], are used when the endpoints are included.

Different Types Of Intervals

Understanding the different types of intervals is key to mastering interval notation. There are primarily four types: open intervals, closed intervals, half-open/half-closed intervals, and time intervals.

Interval Notation

When representing these intervals on a number line, we use interval notation. This is a system that uses brackets and parentheses to denote whether endpoints are included in the interval.

Types of Intervals in Math

To fully grasp this concept, it’s vital to understand the four different types of intervals: open, closed, half-open, and time intervals.

Open Interval

An open interval (a, b) includes all the real numbers between a and b but does not include a and b themselves.

Closed Interval

A closed interval [a, b] includes all the real numbers between a and b, and also includes a and b.

Half-Open and Half-Closed Interval

A half-open or half-closed interval (a, b] or [a, b) includes all the real numbers between a and b, but includes only one endpoint (a or b).

Time Interval

A time interval is a measure of elapsed time between two events. It can also be open, closed, or half-open.

Notations For Different Types of Intervals

The notations for these different types of intervals are crucial for understanding and solving problems using interval notation.

Examples on Interval Notation

Let’s look at a few examples:

  • The open interval (2, 5) includes all real numbers greater than 2 and less than 5. It does not include 2 or 5.

  • The closed interval [2, 5] includes all real numbers greater than or equal to 2 and less than or equal to 5. It includes 2 and 5.

  • The half-open interval (2, 5] includes all real numbers greater than 2 and less than or equal to 5. It includes 5 but not 2.

Practice Questions on Interval Notation

Try these practice questions:

  1. Write the interval notation for all real numbers greater than -3 and less than or equal to 7.
  2. Write the interval notation for all real numbers less than 5.
  3. Write the interval notation for all real numbers greater than or equal to 0.


Embarking on the journey to understand intervals in mathematics, we’ve uncovered an intricate yet fascinating aspect of the subject. Whether it’s expressing a range of numbers or understanding continuity, intervals prove to be a vital concept. Just like our brand Brighterly aims to illuminate the path of learning for children, intervals light up multiple avenues in mathematics.

Understanding intervals and interval notation is a crucial stepping stone in advancing mathematical knowledge. By simplifying complex ranges into a condensed form, interval notation provides a tool that is both elegant and practical. So, as we explore the kingdom of numbers, know that understanding intervals equips us with a valuable tool, just as a lantern guides us through the darkness. Let’s continue to explore, discover, and learn with Brighterly – where learning math is a bright and delightful journey!

Frequently Asked Questions on Interval Notation

What is the interval notation for all real numbers?

  • The interval notation for all real numbers is (-∞, ∞). It means the set of all real numbers includes everything from negative infinity to positive infinity.

What does it mean if an interval is closed?

  • A closed interval means that the end numbers (or endpoints) are included in the interval. For example, in the interval [3, 5], both 3 and 5 are part of the interval along with all the numbers between them.

How do you write an open interval?

  • An open interval is written with parentheses. For example, (3, 5) is an open interval. This means that all the numbers between 3 and 5 are included, but 3 and 5 themselves are not included in the interval.
  1. Wikipedia: Interval (mathematics)
  2. Regents Prep: Interval Notation
  3. Brilliant: Interval Notation

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