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Last updated on July 15th, 2025

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Additive Identity of Rational Numbers

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In rational numbers, zero is known as the additive identity because adding 0 to any number does not change its value. Another important property is the additive inverse. The additive inverse of a number is what you add to it to get zero. Therefore, the additive inverse of any rational number a/b is -a/b.

Additive Identity of Rational Numbers for Saudi Students
Professor Greenline from BrightChamps

What Are Rational Numbers?

Rational numbers are numbers in the form of p/q, where p and q can be any integer and q ≠ 0. Natural numbers, whole numbers, integers, fractions, and decimals (terminating and recurring decimals) are all considered rational numbers. 

 

‘Rational’ is derived from ‘ratio’. Therefore, the idea of fractions, which represent ratios, is closely tied to rational numbers.  In simple words, a number is called rational if it can be written as a fraction where both the numerator and the denominator are integers (the denominator is not zero). 

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What is the Additive Property?

The additive identity property states that adding 0 to a number does not change its value: a + 0 = a. For example, take the rational number ⅖, and its additive inverse is -⅖. According to the property:

 2/5 + (-2/5) = 0

Thus, the property is verified.

 

Two real numbers are said to be additive inverses of each other if their sum equals zero. In general, for any real number R, we have:

 

R + (-R) = 0

 

Here, R and -R are additive inverses of each other. Since rational numbers belong to the set of real numbers, this rule applies to them as well.

 

For example, if you take the rational number ⅚, its additive inverse is -⅚. 
So: 5/6 + (-5/6) = 0. 

 

Here, 5/6 is the additive inverse of -5/6, and vice versa. 

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What Are the Properties of Additive Identity?

The additive identity property states that when you add zero to any number, the value of the number stays the same.

 

  • Zero is the Additive Identity: For any real number a, adding 0 does not change the value of a: a + 0 = a and 0 + a = a.

 

  • Applies to All Numbers: This property holds for all types of numbers, including natural numbers, whole numbers, integers, rational numbers, and real numbers.

 

  • Additive Inverse Relation: Every number a has an additive inverse, which is -a. When you add a number and its additive inverse, the result is always zero.                 
  • Neutral Element in Addition: Zero is called the neutral element in addition because it does not affect the sum.

 

  • Associative and Commutative: The additive identity property follows the associative and commutative properties of addition:

    Associative: (a + b) + 0 = a + (b + 0)

    Commutative: a + 0 = 0 + a
Professor Greenline from BrightChamps

What Are the Additive Identity and Additive Inverse of a Rational Number?

In a mathematical system, the additive identity is an element that, when added to a number, does not change its value. For the set of rational numbers, this identity is 0. The additive identity property states that adding 0 to any number results in the same number:

a + 0 = 0 + a

 

For the additive inverse, a number and its inverse must sum to zero. For example, the additive inverse of -5/7 is 5/7, since:

(-5/7) + (5/7) = 0

 

For the multiplicative inverse, multiplying a number by its reciprocal results in 1. For example, the multiplicative inverse of 4/9 is 9/4, since:

(4/9) × (9/4) = 1

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Real-Life Applications of the Additive Identity of Rational Numbers

The additive identity of rational numbers (0) has practical applications in various real-life situations. Here are a few examples:

 

  • Banking and Finance: When checking your bank balance, adding $0 to your account does not change the total amount. If you have $250 in your account and deposit $0, your balance remains $250.

 

  • Temperature Measurement: If the temperature is 15°C, and there is no change (0°C increase or decrease), the temperature remains 15°C.

 

  • Distance and Travel: If you start at 5 km and don’t move (add 0 km), your position stays the same at 5 km.
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Common Mistakes and How to Avoid Them in Additive Identity of Rational Numbers

While this concept seems simple, students often make common mistakes when applying it. Below are some frequent errors and tips to avoid them.

Mistake 1

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Thinking 1 is the Additive Identity

Students might have a common misunderstanding, which is assuming that 1 is the additive identity.

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Students might have a common misunderstanding, which is assuming that 1 is the additive identity.

Mistake 2

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Confusing Additive Identity with Multiplicative Identity

Some students mix up the two identities, thinking that 0 is the identity for both addition and multiplication.
 

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The additive identity is 0, because a + 0 = a. The multiplicative identity is 1, because a × 1 = a. Both identities apply to different operations.

Mistake 3

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Mixing Up Additive Inverse and Additive Identity


Students might believe that the additive inverse is the same as the additive identity.

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The additive inverse of a is -a, because when you add them together, which is a + (-a) = 0, the result is always zero. On the other hand, the additive identity is simply 0.  

Mistake 4

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Ignoring the Property When Solving Equations

Sometimes, students might forget that adding 0 does not affect the value of a number and change the equation unnecessarily.
 

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Adding 0 makes no difference. For example, x + 0 = x is true for all x.

Mistake 5

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Misapplying the Property to Multiplication

Students might assume that the additive identity works the same for multiplication. For example, a × 0 = a, which is wrong. 

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Students should be taught that the additive identity applies only to addition, not multiplication. In multiplication, any number times 0 is 0, not the original number.

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Solved Examples of Additive Identity of Rational Numbers

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Problem 1

What is the sum of 5/7 and 0?

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5/7 + 0 = 5/7

Explanation

According to the additive identity property, adding 0 to any rational number does not change its value.

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Problem 2

Find the result of (-¾) + 0.

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(-3/4) + 0 = -¾

Explanation

Since 0 is the additive identity, adding it to -¾ keeps the number unchanged.

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Problem 3

Find the result of 0 + 9/11?

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0 + 9/11 = 9/11

Explanation

The order of addition does not matter; adding 0 before or after a number keeps it the same.

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Problem 4

If x + 0 = 2/5, what is the value of x?

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2/5

Explanation

Since adding 0 does not change the number, x must be 2/5.

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Problem 5

A fruit seller has 12.5 kg of apples. If no apples are added to the stock, how much does the stock of apples weigh now?

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12.5 kg + 0 kg = 12.5 kg

Explanation

Adding zero means no change in quantity, so the total remains 12.5 kg. 

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Hiralee Lalitkumar Makwana

About the Author

Hiralee Lalitkumar Makwana has almost two years of teaching experience. She is a number ninja as she loves numbers. Her interest in numbers can be seen in the way she cracks math puzzles and hidden patterns.

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Fun Fact

: She loves to read number jokes and games.

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