在這個部分會學到：
See how the number system was invented and how it works.
數字系統如何被發明以及它如何運作
Identify four important sets of numbers: counting numbers, integers, rational numbers, and real numbers.
辨認四個重要的數字集合：自然數、整數、有理數以及實數
Use place value to write numbers of any size.
使用位值寫下任何大小的數字
Round numbers to make calculating quicker.
使用概數讓計算更迅速
Work with the Big Four operations: adding, subtracting, multiplying, and dividing.
使用四大運算：加、減、乘以及除