Page 48 - ICSE Math 5

Example 9: Find the product of 1,618 and 25 using the expanded form. Check your answer by
actual multiplication.
Solution: 1,618 × 25
Step 1: Write the multiplicand and the multiplier in the expanded form.
1,618 × 25

= (1,000 + 600 + 10 + 8) × (20 + 5)
×
×
Step 2: Multiply each term of the expanded form of the multiplicand by each
term of the expanded form of the multiplier.

= 20 × (1,000 + 600 + 10 + 8) + 5 × (1,000 + 600 + 10 + 8)
× ×
× ×
× ×
× ×
= (20 × 1,000) + (20 × 600) + (20 × 10) + (20 × 8) + (5 × 1,000) + (5 × 600)
+ (5 × 10) + (5 × 8)
Step 3: Find the product of the above numbers. Then add to obtain the final
product.
= 20,000 + 12,000 + 200 + 160 + 5,000 + 3,000 + 50 + 40

= 40,450
So, 1,618 × 25 = 40,450. It is read as forty thousand four hundred fifty.
Check:
Mental Maths
By actual multiplication
Fill in the blanks.
1 1
3 4 (a) _______ × 10 = 2,000
1 6 1 8 (b) 500 × 400 = _______

× 2 5 (c) 250 × 2,000 = _______
(d) 2,568 × 30 = _______
8 0 9 0
1 (e) The standard form of 2,000 + 500
+ 3 2 3 6 0 + 40 + 9 = _______

4 0 4 5 0

So, the multiplication using expanded form is correct.

Exercise 4.1

1. Construct the multiplication tables of the following numbers as per the given instructions.

(a) Multiplication tables of 12 and 15 using repeated addition
(b) Multiplication tables of 14 and 17 using skip counting
(c) Multiplication tables of 18 and 20 by adding 1 to 10

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