Kit Library / Mathematics / Class 9 Ganita Manjari

⚡ Topic Learning Kit

Mock Test Review

English 18 leveled MCQs 18 flashcards 8 games Free

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⚡ Veda Bites

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💡 Key Idea

Rational Number Closure

Division breaks closure for rationals.

Rational numbers are closed under addition, subtraction, and multiplication, meaning the result is always a rational number. However, they are not closed under division because division by zero is undefined, which is not a rational number.

↳ Rational numbers are closed under +, -, × but not ÷ (due to zero).

📖 Definition

Multiplicative Inverse

Zero has no multiplicative inverse.

The multiplicative inverse of a number $x$ is $\frac{1}{x}$, such that $x \times \frac{1}{x} = 1$. Every non-zero rational number has a multiplicative inverse.

↳ Zero is the only rational number without a multiplicative inverse.

💡 Key Idea

Non-Associative Operations

Subtraction and division are not associative.

An operation is associative if $(a \circ b) \circ c = a \circ (b \circ c)$. Addition and multiplication of rationals are associative, but subtraction and division are not.

↳ For rationals, + and × are associative; − and ÷ are not.

📖 Smart notes

What you'll study, topic by topic

1

Class 9 Maths Mock Test: Rational Numbers, AP, GP, Geometry & Polynomials

This mock test covers key Class 9 Maths topics including rational numbers (closure, identities, inverses), arithmetic and geometric progressions, coordinate geometry, polynomials, and circle properties. It tests both con...

  • Rational numbers are closed under +, −, × but not division (by zero).
  • Zero has no multiplicative inverse; 0 is the additive identity.
  • Subtraction and division are not associative for rational numbers.

~8 min · full explanation, examples & memory tricks in the app

❓ Leveled MCQ practice

Try the smart MCQs from this kit

18 questions laddered from warm-up to topper-level, each with an explanation. A taste:

In the standard form of a rational number, the common factor of numerator and denominator is always:

Beginner
A 0 B 1 C -2 D 2
Show answer & explanation

1

A rational number is in standard form when its denominator is positive and the numerator and denominator have no common factor other than 1.

Which of the following is not true for rational numbers?

Beginner
A Rational numbers are closed under multiplication. B Rational numbers are closed under subtraction. C Rational numbers are closed under division. D Rational numbers are closed under addition.
Show answer & explanation

Rational numbers are closed under division.

Rational numbers are not closed under division because division by zero is not defined.

Which of the following numbers does not have a multiplicative inverse?

Beginner
A -1 B 0 C None of these D 1
Show answer & explanation

0

0 does not have a multiplicative inverse because there is no rational number which when multiplied by 0 gives 1.

Which of the following operations is not associative for rational numbers?

Beginner
A Subtraction B Addition C Both (B) and (C) D Division
Show answer & explanation

Both (B) and (C)

Both subtraction and division are not associative for rational numbers. For example, (a - b) - c ≠ a - (b - c).

🃏 Flashcards

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18 flashcards in this kit — the app reviews them with spaced repetition so the right card returns on the right day.

🎮 Learning games

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Word Match True False Memory Match Flashcard Battle Speed Quiz Guess Term Sequence Builder Revision Battle Playable in the app

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