Page 3 - Lesson Note

 Explanation: Addition : [ Take Three whole numbers 10, 5 and 6 ]

Case 1: 10 + 5 + 6

= (10 + 5) + 6 ( The sum of 10 and 5 grouped first)

= 15 + 6 = 21 ( Then 6 is added to the sum)

Case 2: 10 + 5 + 6

= 10 + (5 + 6) ( Sum of 5 and 6 grouped first)

= 10 + 11 = 21 ( Then 10 is added to the sum)

(10 + 5) + 6 = 10 + (5 + 6)

Whole numbers 10,5 and 6 can be grouped in any order and added, the result will be the
same ,

 Explanation: Multiplication: [ Take Three whole numbers 10, 5 and 6 ]

Case 1: 10 × 5 × 6

= (10 × 5) × 6 ( Product of 10 and 5 grouped first)

= 50 × 6 = 300 ( Then 6 is multiplied to the product)

Case 2: 10 × 5 × 6

= 10 × (5 × 6) (Product of 5 and 6 grouped first)

= 10 × 11 = 21 ( Then 10 is multiplied to the product)

(10 × 5) × 6 = 10 × (5 × 6)

Whole numbers 10,5 and 6 can be grouped in any order and multiplied, the result will be the

same .

NOTE: Associative property for division of whole numbers does not hold true.

Some more examples:

Find the sum by suitable rearrangement ( NCERT Ex-2.2)

Q1. (b) 1962 + 453 + 1538 + 647

= (1962+1538) + (453 + 647) [ Hint: Sum of 1962+1538 gives a

number ending with zero, which helps
next step of addition]

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