Page 80 - ICSE Math 6

LCM of 5 and 4 = 20

33 33×4 132
\ = = (20 ÷ 5 = 4)
5 5×4 20
15 = 15×5 = 75
4 4×5 20 (20 ÷ 4 = 5)

3 3 33 15 132 75 57 17
\ 6 − 3 = − = − = = 2
5 4 5 4 20 20 20 20
3 3  3 3 
Alternatively, 6 − 3 = (6 3)− +  − 
5 4  5 4 

 3×4 3×5   12 15 
= 3+  −  = 3+  − 
 5×4 4×5   20 20 

 3   3   20 3−  17 17
= 3+ −  = 2 +  1−  = 2 +   = 2 + = 2

 20   20   20  20 20

Multiplication of fractions
To multiply a fraction with another fraction, multiply their numerators to get the numerator of the
resulting fraction and multiply their denominators to get the denominator of the resulting fraction.
Convert the resulting fraction to the lowest form, if needed. Alternatively, we can cancel out the
common factors from the numerator and denominator of the fractions and then multiply to get the
required product.

Before multiplying fractions, convert every mixed fraction into an improper fraction.

Example 19: Multiply.
3 10 5 1 15
(a) by (b) by14 (c) 3 by
5 27 7 5 4
3 10 3×10 30 2
Solution: (a) × = = =
5 27 5×27 135 9

3 10 1 3 × 10 2 2
Alternatively, × = =
5 27 1 5 × 27 9 9

5 5 14 5×14 70
(b) ×14 = × = = = 10
7 7 1 7×1 7
5 5× 14 2
Alternatively, ×14 = = 10
7 1 7 ×1
1 (3×5) 1 16+
(c) As, 3 = =
5 5 5
1 15 16 15 16×15 240
\ 3× = × = = = 12
5 4 5 4 5×4 20

1 15 16 15 4 16 × 15 3
Alternatively, 3× = × = = 12
5 4 5 4 1 5 × 4 1

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