**Natural Numbers:**

The natural numbers include whole numbers except 0.

E.g. 1,2,3,4,5,6…

**Integers:**

Positive natural numbers, negative natural numbers along with 0 are called integers.

-1,-2,-3,0,+1,+2,+3…

**Prime Numbers:**

A prime number is a number with exactly two factors (i.e. 1 and itself (1×3))

E.g. 2,3,5,7,111,13,17,19,23,29,31…

**Composite Numbers:**

Those numbers which have more than two factors.

E.g. 1,4,6,8,9,10,12,14,15,16,18,20…

**Factors:**

The factors of a number are the natural numbers which divide exactly into that number (without a remainder).

**8:** 1×8 **12:** 1×12

2×4 2×6

3×4

**Multiples:**

Multiples of a number are numbers in its times table.

Multiples of 5 are 5, 10, 15, 20, 25, 30…

** **

**Highest Common Factor (HCF):**

It is the highest factor which is common to all of the given numbers.

E.g. **8:** 1×8 **12:** 1×12

2×__4__ 2×6 In this example the common factors are 1, 2, 4 and the

3×__4__ Highest factor is 4; therefore the HCF of 12 and 8 is 4.__ __

In this example the common factors are 1, 2, 4 and the highest factor is 4; therefore the HCF of 12 and 8 is 4.__ __

**Rational Number:**

A rational number is one which can be expressed in the form where a and b are integers and b is not equals to 0.

**Irrational Number:**

Numbers that can’t be expressed as as a fraction or a ratio of 2 integers are known as irrational numbers.

**Real Numbers:**

These include all rational, irrational, fractions and integers.

**Terminating Decimals:**

These are decimal numbers which stop after a certain number of decimal places.

E.g. 7/8 = 0.875 it stops after three decimal places.

**Recurring Decimals:**

These are decimal numbers which keep repeating a digit or a group of digits.

E.g. 137/259 = 0.528 957 528 957 528 957… the six digits 528 957 repeat in this order.

**Even Number:**

Numbers which are divisible by 2

E.g. 2, 4, 6, 8…

**Odd Number:**

Numbers which are not divisible by 2

E.g. 1, 3, 5, 7

**Square Number:**

It is the result of multiplying a number by itself.

E.g. 1^{2}, 2^{2}, 3^{2} ….. 1, 4, 9….

**Cube Number:**

It is the result of multiplying a number by itself 3 times.

E.g. 1^{3}, 2^{3}, 3^{3} …. 1, 8, 27….

**Significant Figures:**

The following are few examples showing clearly what is meant by significant figures.

8064 = 8000 (correct to 1 significant figures)

8064 = 8100 (correct to 2 significant figures)

8064 = 8060 (correct to 3 significant figures)

0.00208 = 0.005 (correct to 1 significant figures)

0.00208 = 0.0021 (correct to 2 significant figures)

3.00508 = 3.01 (correct to 3 significant figures)

**Decimal Places:**

The following are few examples showing clearly what is meant by decimal places.

0.0647 = 0.1 (correct to 1 dp)

0.0647 = 0.06 (correct to 2dp)

0.0647 = 0.065 (correct to 3dp)

2.0647 = 2.065 (correct to 3dp)