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.
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. 12, 22, 32 ….. 1, 4, 9….
Cube Number:
It is the result of multiplying a number by itself 3 times.
E.g. 13, 23, 33 …. 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)
Test Of Divisibility:
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