Math Vocabulary
Topic 2 - Adding Whole Numbers
Lesson 2-1 Addition Meaning and Properties
Commutative (Order) Property of Addition: You can add numbers in any order and the sum will be the same.
7 + 5 = 5 + 7
Identity (Zero) Property of Addition: The sum of zero and any number is that same number.
5 + 0 = 5
Associative (Grouping) Property of Addition: You can group addends in any way and the sum will be the same.
(3 + 4) + 5 = 3 + (4 + 5)
Parentheses,(), show what to add first.
Addends: Numbers being added together
Sum: Answer when adding
Lesson 2-4 Rounding
Round To round, replace a number with a number that tells about how many.
When we round to the nearest 10, use numbers such as 10, 20, 30.
Look at the number to the right.
If the number to the right is 5,6,7,8,or 9, round up to the next higher 10.
395 rounds to 400
426 rounds to 430
If the number to the right is 0,1,2,3, or 4, round down to the lower 10.
394 rounds to 390
421 rounds to 420
--------------------------------------------------------------------------------
When we round to the nearest hundred, use numbers such as 100, 200, or 300.
Look at the number to the right.
If the number to the right is 5,6,7,8,or 9, round up to the next higher 100.
395 rounds to 400
454 rounds to 500
If the number to the right is 0,1,2,3,or 4, round down to the lower 100.
346 rounds to 300
427 rounds to 400
Lesson 2-5 Estimating Sums
estimate: You can estimate to find out about how much.
compatible numbers: Numbers that are close to the addends, but easy to add mentally.
Use compatible numbers to help estimate:
255 -------------- 250
+ 322 -------------- + 325
575
255 + 322 is about 575
Lesson 2-1 Addition Meaning and Properties
Commutative (Order) Property of Addition: You can add numbers in any order and the sum will be the same.
7 + 5 = 5 + 7
Identity (Zero) Property of Addition: The sum of zero and any number is that same number.
5 + 0 = 5
Associative (Grouping) Property of Addition: You can group addends in any way and the sum will be the same.
(3 + 4) + 5 = 3 + (4 + 5)
Parentheses,(), show what to add first.
Addends: Numbers being added together
Sum: Answer when adding
Lesson 2-4 Rounding
Round To round, replace a number with a number that tells about how many.
When we round to the nearest 10, use numbers such as 10, 20, 30.
Look at the number to the right.
If the number to the right is 5,6,7,8,or 9, round up to the next higher 10.
395 rounds to 400
426 rounds to 430
If the number to the right is 0,1,2,3, or 4, round down to the lower 10.
394 rounds to 390
421 rounds to 420
--------------------------------------------------------------------------------
When we round to the nearest hundred, use numbers such as 100, 200, or 300.
Look at the number to the right.
If the number to the right is 5,6,7,8,or 9, round up to the next higher 100.
395 rounds to 400
454 rounds to 500
If the number to the right is 0,1,2,3,or 4, round down to the lower 100.
346 rounds to 300
427 rounds to 400
Lesson 2-5 Estimating Sums
estimate: You can estimate to find out about how much.
compatible numbers: Numbers that are close to the addends, but easy to add mentally.
Use compatible numbers to help estimate:
255 -------------- 250
+ 322 -------------- + 325
575
255 + 322 is about 575