2 The Steps: Line up the numbers by the decimal point. Fill in missing places with zeroes.Add or subtract.
3 Addition PropertiesCommutative Property of Addition: Numbers can be added in any order.Example: 5+3=3+5Associative Property of Addition: Numbers can be grouped in any way.Example: (7+3) + 5 = 7 + (3+5)Identity Property of Addition: The sum of any number and zero is that number.Example: = 18
4 Mental Math Addition properties can be used to quickly find sums. Example: What is ?We can use an addition property to quickly add this.First, change the order: ________________ property.Then, group the first two addends together: ( ) ________________ property= 112.4commutativeassociative
5 Why Estimate?Before adding your numbers, use one of the estimating strategies you learned. When you add, you can see if your answer is reasonable.
6 Example:This can estimate to , which is 43. (Compatible numbers)28.9+13.3142.21The answer is close to the estimate.
7 Subtracting The addition properties do not work for subtraction. Estimate and subtract to find the answer to which it is closest.Subtract to find the real answer.
8 Subtracting Across Zeroes If you have several zeroes in a row, and you need to regroup, go to the first digit that is not zero, and borrow.All middle zeroes become 9s.The final zero becomes 10.