Grade 3

Theory:

Inverse Relationship between Multiplication and Division

There is an inverse relationship between multiplication and division just like there was between addition and subtraction.

The equation 3 × 7 = 21 has the inverse relationships:
21 ÷ 3 = 7
21 ÷ 7 = 3

Similar relationships exist for division. The equation 45 ÷ 5 = 9 has the inverse relationships:
5 × 9 = 45
9 × 5 = 45

Solutions from the Previous Issue:

1. Let a = 6 × 8 + 2 × 9 + 6 × 4; b = 6 × 8 – 2 × 9 - 6× 4;

Calculate the sum and the difference of the two numbers.

Solution:

a = 6 × 8 + 2× 9 + 6 × 4 = 48 + 18 + 24 = 90

b = 6 × 8 - 2× 9 - 6× 4 = 48 - 18 - 24 = 6

a + b = 96

a – b = 90 – 6 = 84

2. Calculate: A = (7 × 8 – 20) ÷ 6 + 100 ÷ 4 – 20

Solution:

A = (7 × 8 – 20) ÷ 6 + 100 ÷ 4 – 20 = (56 – 20) ÷ 6 + 25 – 20 = 36 ÷ 6 + 25 – 20 = 6 + 25 – 20 = 11

Verify the followings equalities: