Page 88 - ICSE Math 5

1
Example 23: Multiply 3 by 18.
4
9
1 (3 × 4) + 1 13 × 18
Solution: 3 × 18 = × 18 = (2 is a common factor of 18 and 4.)
4 4 4
2
13 × 9 117 1
= = = 58
2 2 2
Fraction of a Whole Number

2 1
Example 24: What is of 6? Example 25: What is of ` 20?
3 5
2 2 2  6 12 1 1  20 20
Solution: of 6 = × 6 = = = 4 Solution:  20 = = = 4
3 3 3 3 5 5 5
2 1
So, of 6 = 4. So, of ` 20 = ` 4.
3 5
Multiplication of a Fraction by Another Fraction

To multiply a fraction by another fraction, we follow the given steps.
• Multiply the numerators of the two fractions to obtain a new numerator.
• Multiply the denominators of the two fractions to obtain a new denominator.

• Reduce the fraction to the lowest terms, if required. In case of an improper fraction, change
to mixed fraction.
Example 26: Multiply the following fractions.
2 3 9 7 1 4
(a) by (b) by (c) 5 by 2
7 5 11 18 3 5
1
2 3 2  3 6 9 7 9  7 1  7 7
Solution: (a) × = = (b) × = = =
7 5 7  5 35 11 18 11  18 11  2 22
1 4 (5 × 3) + 1 (2 × 5) + 4 2
(c) 5 × 2 = ×
3 5 3 5
16 14 16 × 14 224 14
= × = = = 14
3 5 3 × 5 15 15

Properties of Multiplication of Fractions

• Two fractions can be multiplied in any order as their product remains the same.
3 4 12 4 3
For example, × = = × .
7 5 35 5 7
• Three fractions can be multiplied by grouping them in any order.
2 5 3 2 5 3
For example, × × = × × .
3 6 4 3 6 4
• The product of a fraction and 0 is always 0.
1
For example, × 0 = 0.
10
• The product of a fraction and 1 is always the fraction itself.
1 1
For example, × 1 = .
8 8

78