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CBSE · Class 7 · 🧮 Maths · Chapter 8

WORKING WITH FRACTIONS

Multiplication of FractionsDivision of FractionsReciprocal of a FractionProduct of FractionsSimplifying FractionsFraction Word Problems

Chapter 8, 'Working with Fractions', introduces students to the fundamental operations of multiplication and division involving fractions. You will learn how to multiply a whole number by a fraction, multiply two fractions, understand the concept of a reciprocal, and apply these operations to solve real-world problems. This chapter builds a strong foundation for more advanced topics in mathematics by clarifying how fractions behave under these essential operations.

Multiplying a Whole Number by a Fraction

Tortoise ki speed ka example
Tortoise ki speed ka example
Fraction ka visual representation
Fraction ka visual representation

Jab hum ek whole number ko fraction se multiply karte hain, toh basically hum us fraction ko utni baar repeat kar rahe hote hain.

  • Concept: Whole Number × Fraction ka matlab hai Fraction ko Whole Number times add karna.
  • Example: 3 × 1/4 ka matlab 1/4 + 1/4 + 1/4.
  • Method:
  1. Whole number ko fraction ke numerator se multiply karo.
  2. Denominator same rakho.
  • Formula: a × (b/c) = (a × b) / c
  • Visualisation:
  • Imagine karo ek cake hai, uske 4 equal parts hain. Agar tum 1/4th part 3 baar lete ho, toh total 3/4th part liya.
  • [IMAGE: multiplying_fractions_on_a_number_line_fig1] mein dekho, tortoise 1/4 km chalta hai 1 hour mein. 3 hours mein 3 × 1/4 = 3/4 km chalta hai.
  • Mixed Fractions ke saath:
  • Agar mixed fraction hai, toh pehle usko improper fraction mein convert karo.
  • Phir whole number se multiply karo.
  • Example: 2 × 1(1/2) = 2 × (3/2) = (2 × 3) / 2 = 6/2 = 3.

Simplification: Agar numerator aur denominator mein koi common factor ho, toh multiplication se pehle ya baad mein simplify kar sakte hain. Pehle simplify karna usually easier hota hai.

🧮Formula

Multiplication of Whole Number and Fraction: Whole Number × (Numerator / Denominator) = (Whole Number × Numerator) / Denominator Example: 5 × (2/7) = (5 × 2) / 7 = 10/7

Remember

Of ka matlab maths mein multiplication hota hai. Jaise 1/2 of 10 ka matlab 1/2 × 10.

Multiplying Two Fractions

Visualizing 1/2 × 1/4
Visualizing 1/2 × 1/4
Area model for fraction multiplication
Area model for fraction multiplication
Order of multiplication
Order of multiplication

Do fractions ko multiply karna matlab ek fraction ka part nikalna.

  • Concept: 1/2 of 1/4 ka matlab 1/2 × 1/4.
  • Imagine karo ek square hai, uske 1/4th part ko shade kiya. Ab us shaded part ka 1/2 nikalna hai. Toh woh original square ka 1/8 part hoga.
  • [IMAGE: visualizing_fraction_multiplication_fig5] aur [IMAGE: visualizing_fraction_multiplication_fig83] mein isko visually samjhaya gaya hai.
  • Method:
  1. Numerators ko multiply karo.
  2. Denominators ko multiply karo.
  • Formula: (a/b) × (c/d) = (a × c) / (b × d)
  • Historical Context: Ye formula Brahmagupta ne 628 CE mein apne 'Brāhmasphuṭasiddhānta' mein diya tha.
  • Simplification:
  • Multiplication se pehle cross-cancellation kar sakte hain. Numerator aur opposite denominator mein common factor ho toh unhe divide kar do.
  • Example: (2/3) × (3/4) = (2/4) = 1/2 (yahan 3 se 3 cancel ho gaya, aur 2/4 simplify ho gaya).
  • Area of Rectangle: Fractional sides wale rectangle ka area nikalne ke liye sides ko multiply karte hain. Area = Length × Breadth.
  • Example: Length = 1/2 unit, Breadth = 1/4 unit. Area = (1/2) × (1/4) = 1/8 square units.
  • Order of Multiplication (Commutative Property): Fractions ke multiplication mein order matter nahi karta. (a/b) × (c/d) = (c/d) × (a/b).
  • [IMAGE: order_of_multiplication_of_fractions_figorderofmultiplication] is property ko dikhata hai.
🧮Formula

Multiplication of Two Fractions (Brahmagupta's Formula): (a/b) × (c/d) = (a × c) / (b × d) Example: (3/5) × (1/2) = (3 × 1) / (5 × 2) = 3/10

💡Tip

Multiplication se pehle cross-cancellation karne se calculations easy ho jaati hain aur mistakes kam hoti hain. Always check for common factors diagonally.

Product of Fractions and its Relation to Numbers Multiplied

Fraction multiplication ke results ko original numbers se compare karna important hai.

  • Case 1: Dono numbers > 1
  • Agar dono fractions 1 se bade hain (ya mixed numbers hain), toh product dono numbers se bada hoga.
  • Example: 2 × 3 = 6 (6 > 2, 6 > 3)
  • Example: 1(1/2) × 2(1/3) = (3/2) × (7/3) = 7/2 = 3(1/2) (3.5 > 1.5, 3.5 > 2.33)
  • Case 2: Dono numbers 0 aur 1 ke beech mein
  • Agar dono fractions 0 aur 1 ke beech mein hain (proper fractions), toh product dono numbers se chhota hoga.
  • Example: (1/2) × (1/4) = 1/8 (1/8 < 1/2, 1/8 < 1/4)
  • Ye 'of' concept se samjha ja sakta hai: 1/2 of 1/4 matlab 1/4 ka bhi aadha, toh aur chhota ho gaya.
  • Case 3: Ek number 0 aur 1 ke beech, aur doosra > 1
  • Product 1 se bade number se chhota hoga, aur 0 se 1 ke beech wale number se bada hoga.
  • Example: 2 × (1/2) = 1 (1 < 2, 1 > 1/2)
  • Example: 5 × (1/4) = 5/4 = 1(1/4) (1.25 < 5, 1.25 > 0.25)

Ye observations estimation aur checking answers ke liye useful hain.

Important

Product ki Comparison:

  • Fraction > 1 aur Fraction > 1 $\implies$ Product > dono fractions
  • Fraction < 1 aur Fraction < 1 $\implies$ Product < dono fractions
  • Fraction < 1 aur Fraction > 1 $\implies$ Product < Fraction > 1 aur Product > Fraction < 1

Reciprocal of a Fraction

Reciprocal ka concept division of fractions mein bahut important hai.

  • Definition: Ek fraction ka reciprocal woh fraction hota hai jisko original fraction se multiply karne par product 1 aata hai.
  • Simply, numerator aur denominator ko interchange kar do.
  • Example: 2/3 ka reciprocal 3/2 hai, kyunki (2/3) × (3/2) = 6/6 = 1.
  • Whole Numbers ka Reciprocal:
  • Kisi whole number a ko a/1 likh sakte hain.
  • Toh a ka reciprocal 1/a hoga.
  • Example: 5 ka reciprocal 1/5.
  • Mixed Fractions ka Reciprocal:
  • Pehle mixed fraction ko improper fraction mein convert karo.
  • Phir improper fraction ka reciprocal nikaalo.
  • Example: 1(2/3) = 5/3. Iska reciprocal 3/5.
  • Important Points:
  • 0 ka koi reciprocal nahi hota, kyunki 1/0 undefined hai.
  • 1 ka reciprocal 1 hai.
  • -1 ka reciprocal -1 hai.

Reciprocal ko multiplicative inverse bhi kehte hain.

📖Definition

Reciprocal (Multiplicative Inverse): Ek fraction a/b ka reciprocal b/a hota hai. Jab a/b ko b/a se multiply karte hain, toh result 1 aata hai. Example: 7/9 ka reciprocal 9/7.

🚧Misconception

Students aksar mixed fraction ka reciprocal seedha ulta kar dete hain, jaise 1(2/3) ka 1(3/2) bol dete hain. Ye galat hai! Pehle improper fraction mein convert karna zaroori hai.

Division of Fractions

Dividing a fraction by a whole number
Dividing a fraction by a whole number
Visualizing division of fractions
Visualizing division of fractions
Division of Fractions and Reciprocals
Division of Fractions and Reciprocals

Fractions ko divide karna matlab reciprocal se multiply karna.

  • Concept: Division ko multiplication mein convert kiya ja sakta hai.
  • 12 ÷ 4 ka matlab hai 4 × ? = 12. Answer 3.
  • 1 ÷ (2/3) ka matlab hai (2/3) × ? = 1. Yahan ? reciprocal 3/2 hoga.
  • Method (Keep, Change, Flip - KCF):
  1. Keep the first fraction (dividend) as it is.
  2. Change the division sign ÷ to multiplication sign ×.
  3. Flip the second fraction (divisor) to its reciprocal.
  • Formula: (a/b) ÷ (c/d) = (a/b) × (d/c) = (a × d) / (b × c)
  • Historical Context: Ye method bhi Brahmagupta ne hi apne 'Brāhmasphuṭasiddhānta' mein explain kiya tha.
  • Division of a Whole Number by a Fraction:
  • Whole number ko a/1 ki form mein likho.
  • Phir KCF method apply karo.
  • Example: 5 ÷ (1/2) = (5/1) × (2/1) = 10/1 = 10.
  • Division of a Fraction by a Whole Number:
  • Whole number ko a/1 ki form mein likho.
  • Phir KCF method apply karo.
  • Example: (3/4) ÷ 2 = (3/4) ÷ (2/1) = (3/4) × (1/2) = 3/8.
  • [IMAGE: dividing_a_fraction_by_a_whole_number_fig81] aur [IMAGE: visualizing_32_divided_by_4_fig82] mein isko visually samjhaya gaya hai.
  • Quotient ki Comparison:
  • Whole numbers mein Dividend ÷ Divisor mein quotient aksar dividend se chhota hota hai (e.g., 6 ÷ 3 = 2).
  • Fractions mein aisa hamesha nahi hota. Agar divisor 1 se chhota hai, toh quotient dividend se bada ho sakta hai.
  • Example: 6 ÷ (1/2) = 12 (12 > 6).
  • Example: (1/2) ÷ (1/4) = 2 (2 > 1/2).
  • Agar divisor 1 se bada hai, toh quotient dividend se chhota ho sakta hai.
  • Example: (1/2) ÷ 2 = 1/4 (1/4 < 1/2).
🧮Formula

Division of Fractions (KCF Method): (a/b) ÷ (c/d) = (a/b) × (d/c) Example: (3/4) ÷ (1/5) = (3/4) × (5/1) = 15/4

💡Tip

Word problems mein 'how many times' ya 'how many parts' jaise phrases aksar division indicate karte hain. Dhyan se padho ki kaunsa fraction dividend hai aur kaunsa divisor.

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