It is important that children recognise the relationship between addition and subtraction as early as possible as this will make their mental skills much faster. By relationships we mean that if one fact is known then several others can be realised. For example if it is known that 5 + 4 = 9 then the following three facts can be deduced: 4 + 5 = 9 9 - 5 = 4 9 - 4 = 5 Knowing this relationship increases your knowledge four fold! Know other addition and subtraction facts