Multiplication of Rational Numbers

To learn multiplication of rational numbers let us recall how to multiply two fractions. The product of two given fractions is a fraction whose numerator is the product of the numerators of the given fractions and whose denominator is the product of the denominators of the given fractions.

In other words, product of two given fractions = product of their numerators/product of their denominators

Similarly, we will follow the same rule for the product of rational numbers.

Therefore, product of two rational numbers = product of their numerators/product of their denominators.

Thus, if a/b and c/d are any two rational numbers, then

a/b × c/d = a × c/b × d

Solved examples on multiplication of rational numbers:

1. Multiply 2/7 by 3/5

Solution:

2/7 × 3/5

= 2 × 3/7 × 5

= 6/35

2. Multiply 5/9 by (-3/4)

Solution:

5/9 × (-3/4)

= 5 × -3/9 × 4

= -15/36

= -5/12

3. Multiply (-7/6) by 5

Solution:

(-7/6) × 5

= (-7/6) × 5/1

= -7 × 5/6 × 1

= -35/6

4. Find each of the following products:

(i) -3/7 × 14/5

(ii) 13/6 × -18/91

(iii) -11/9 × -51/44


Solution:

(i) -3/7 × 14/5

= {(-3) × 14/(7 × 5)

= -6/5

(ii) 13/6 × -18/91 

= {13 × (-18)}/(6 × 91)

= -3/7


(iii) -11/9 × 51/44

= {(-11) × (-51)}/(9 × 44)

= 17/12


5. Verify that:

(i) (-3/16 × 8/15) = (8/15 × (-3)/16)

(ii) 5/6 × {(-4)/5 + (-7)/10} = {5/6 × (-4)/5} + {5/6 × (-7)/10}


Solution:

(i) LHS = ((-3)/16 × 8/15) = {(-3) × 8}/(16 × 15) = -24/240 = -1/10

RHS = (8/15 × (-3)/16) = {8 × (-3)}/(15 × 16) = -24/240 = -1/10

Therefore, LHS = RHS.

Hence, ((-3)/16 × 8/15) = (8/15 × (-3)/16)


(ii) LHS = 5/6 × {-4/7 + (-7)/10} = 5/6 × [{(-8) + (-7)}/10}

= 5/6 × (-15)/10

= 5/6 × (-3)/2 = {5 × (-3)}/(6 × 2) = -15/12 = -5/4

RHS = {5/6 × -4/5} + {5/6 ×(-7)/10}

= {5 × (-4)/(6 × 5) + { 5 × (-7)}/(6 × 10) = -20/30 + (-35)/60

= (-2)/3 + (-7)/12

= {(-8) + (-7) }/ 12 = (-15)/12 = (-5)/4

Therefore, LHS = RHS

Hence, 5/6 × (-4/5 + (-7)/10) = {5/6 × (-4)/5} + (5/6 × (-7)/10)

● Rational Numbers

Introduction of Rational Numbers

What is Rational Numbers?

Is Every Rational Number a Natural Number?

Is Zero a Rational Number?

Is Every Rational Number an Integer?

Is Every Rational Number a Fraction?

Positive Rational Number

Negative Rational Number

Equivalent Rational Numbers

Equivalent form of Rational Numbers

Rational Number in Different Forms

Properties of Rational Numbers

Lowest form of a Rational Number

Standard form of a Rational Number

Equality of Rational Numbers using Standard Form

Equality of Rational Numbers with Common Denominator

Equality of Rational Numbers using Cross Multiplication

Comparison of Rational Numbers

Rational Numbers in Ascending Order

Rational Numbers in Descending Order

Representation of Rational Numbers on the Number Line

Rational Numbers on the Number Line

Addition of Rational Number with Same Denominator

Addition of Rational Number with Different Denominator

Addition of Rational Numbers

Properties of Addition of Rational Numbers

Subtraction of Rational Number with Same Denominator

Subtraction of Rational Number with Different Denominator

Subtraction of Rational Numbers

Properties of Subtraction of Rational Numbers

Rational Expressions Involving Addition and Subtraction

Simplify Rational Expressions Involving the Sum or Difference

Multiplication of Rational Numbers

Product of Rational Numbers

Properties of Multiplication of Rational Numbers

Rational Expressions Involving Addition, Subtraction and Multiplication

Reciprocal of a Rational  Number

Division of Rational Numbers

Rational Expressions Involving Division

Properties of Division of Rational Numbers

Rational Numbers between Two Rational Numbers

To Find Rational Numbers

8th Grade Math Practice

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