Chapter: 3rd Maths : Term 2 Unit 1 : Numbers
Multiplication by Regrouping
Understanding Multiplication Methods
Multiplication of a number with other number can be done in the following ways.
(i) Dot multiplication
(ii) Repeated addition
(iii) Regrouping
(iv) Standard multiplication algorithm
(v) Lattice multiplication
Multiplication by Regrouping
This method can be used by multiplying a two digit number.
Consider the following multiplication:
53 × 7
53 can be regroup into 5 tens and 3 ones.
Hence, 53 × 7 can be written as (50 + 3) × 7
= (50 × 7) + (3 × 7)
= 350 + 21
= 371.
Example
14 × 2 = ?
That is 2 Times 14
14 × 2 = 2 × 1 Ten + 2 × 4 Ones
= 2 × 10 + 2 × 4 = 20 + 8
= 14 × 2 = 28
Exercise
1. Multiply the following numbers by regrouping
(i) 75 × 8
= (70 + 5) × 8
= (70 × 8) + (5 × 8)
= 560 + 40
= 600
(ii) 26 × 5
= (20 + 6) × 5
= (20 × 5) + (6 × 5)
= 100 + 30
= 130
(iii) 372 × 6
= (370 + 2) × 6
= (370 × 6) + (2 × 6)
= 2220 + 12
= 2232
(iv) 402 × 7
= (400 + 2) × 7
= (400 × 7) + (2 × 7)
= 2800 + 14
= 2814
(v) 752 × 3
= (750 + 2) × 3
= (750 × 3) + (2 × 3)
= 2250 + 6
= 2256