Mathematics Grade 7 15 min

Multiplicative inverses

Multiplicative inverses

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Introduction & Learning Objectives

Learning Objectives Define multiplicative inverse and reciprocal. Find the multiplicative inverse of any non-zero whole number. Find the multiplicative inverse of any non-zero fraction. Find the multiplicative inverse of any non-zero mixed number. Find the multiplicative inverse of any non-zero decimal. Explain why the product of a number and its multiplicative inverse is always 1. Apply the concept of multiplicative inverses to simplify expressions. Ever wonder how to 'undo' multiplication? 🤔 What if you wanted to get back to 1 after multiplying a number? In this lesson, you'll discover multiplicative inverses, also known as reciprocals. These special numbers help us understand division, simplify fractions, and solve equations, making math much clearer an...
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Key Concepts & Vocabulary

TermDefinitionExample Multiplicative InverseA multiplicative inverse of a number is another number that, when multiplied by the first number, results in a product of 1. It 'undoes' the multiplication.The multiplicative inverse of 5 is 1/5, because 5 × (1/5) = 1. ReciprocalReciprocal is another name for the multiplicative inverse. To find the reciprocal of a fraction, you 'flip' it (swap the numerator and denominator).The reciprocal of 2/3 is 3/2. ProductThe result obtained when two or more numbers are multiplied together.In 4 × 3 = 12, the number 12 is the product. Identity Property of MultiplicationThis property states that any number multiplied by 1 remains that same number. The number 1 is called the multiplicative identity.7 × 1 = 7, and 1 × (-3) = -3. Unit Fractio...
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Core Formulas

Definition of Multiplicative Inverse $a \times \frac{1}{a} = 1 \quad \text{for } a \neq 0$ This rule defines what a multiplicative inverse is: any non-zero number multiplied by its inverse equals 1. This applies to whole numbers, fractions, and decimals. Reciprocal of a Fraction \text{The reciprocal of } \frac{a}{b} \text{ is } \frac{b}{a} \quad \text{for } a, b \neq 0$ To find the reciprocal of a fraction, simply swap its numerator and denominator. This 'flips' the fraction. Reciprocal of a Whole Number \text{The reciprocal of } a \text{ is } \frac{1}{a} \quad \text{for } a \neq 0$ To find the reciprocal of a whole number, write it as a fraction with 1 as the denominator (e.g., $a = a/1$), then flip it.

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Sample Practice Questions

Challenging
What is the multiplicative inverse of -7/11?
A.11/7
B.7/11
C.-11/7
D.1
Challenging
Find the multiplicative inverse of -1 3/5.
A.-5/8
B.-8/5
C.1 5/3
D.5/8
Challenging
If (9/2) × y = 1, what is the value of y?
A.1
B.-9/2
C.9/2
D.2/9

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