# operations with Natural Numbers

2 + 2 = 4    two plus two equals/is four
6 – 4 = 2    six minus four equals/is two

Bracket use: Remember that you must do the operations in brackets first.

Example:
9 – 1 + 3= 11 9 - (1 + 3) = 9 – 4 = 5

- Commutative property:
3 + 5 = 5 + 3
- Associative property:
(2 + 3) + 7 = 2 + (3 + 7)

MULTIPLICATION

The multiplication is a repeated addition:
35 + 35 + 35 = 3 · 35 = 105        three by thirty-five or three times thirty-five equals one hundred and five

Multiplication properties:
· Commutative property: 3 · 5 = 5 · 3
· Associative property: (2 · 3) · 5 = 2 · (3 · 5)
· Distributive property:     3 · (4 + 5) = 3 · 4 + 3 · 5              (7 – 3) · 2 = 7 · 2 – 3 · 2

DIVISION

To divide is to distribute in equal parts:
150: 6 = 25       one hundred and fifty divided by six equals twenty-five.

The division is exact when the remainder equals zero. When the remainder doesn't equal zero we call it whole division.

Remember:

 D = d · q + r

And now, you can play and practise the multiplication and division:

Exercise
Calculate:

a) 3 + 5 + 7 - 11 - 2 + 10 =

b) 5 - (3 + 1) + 2 - (8 - 6) + 3 =

c) 25 · 2 · 3 = 150

d) 48 : 12 =

e) 72 : 12 : 3 =

f) Calculate the quotient and remainder of the division: 1482 : 15

Quotient =      Remainder =