Number sense is a good intuition about numbers and their relationships. It is all about understanding how our numbers work and how the parts and wholes come together.
We need to have 4 relationships to develop a sense of numbers.
1) Spatial Relationship: It is defined as having a visual to go with a numeral and relate both of them.
Here, we see that 3 dots represent three and 4 dots represent four.
2) One/Two more and less: Here we need to instantly know the amount that is one or two more or less.
From the figure we can see that adding one to four will give us five and subtracting one will give us three.
3) Part-part-whole: We need to understand how a whole can be broken into parts and vice versa.
For example, we can break the number 7 as follows:
We also need to know when to break seven into 1 and 6 versus a 2 and 5. What is the point of being able to break that apart?
4) Benchmarks of five and ten: We need to know how a number relates to 5 and 10. The best way to do that is by visual explanation.
Let us assume that we need to add the numbers 8 and 5 and get a number 10. For that we can break 8 into 3 and 5. So, that we get the answer as three plus ten.
This way we can think of breaking the numbers.