How to add numbers 
How to subtract numbers 
How to multiply numbers 
How to divide numbers 

Divisibility rules 
Multiples of a number 
Lowest Common Multiple / Least Common Multiple 
Highest Common Factor / Greatest Common Factor 

What are fractions 
Types of fractions 
Like fraction operations 
Unlike fractions 

Decimal numbers 
Decimal numbers operations  addition & subtraction 
Decimal numbers operations  multiplication & division 