Topic 2
作者：Jolene Tappe
1. Rounding
2. Estimating
2.1. compatible numbers
2.2. rounded numbers
3. Compatible Numbers
4. Vocabulary
4.1. addend
4.1.1. The numbers that are added together to find a sum
4.2. sum
4.2.1. The number that is the result of adding two or more addends
4.3. difference
4.3.1. The number that results from subtracting one number from another.
4.4. whole numbers
4.4.1. The numbers 0,1,2,3,...