That's my property!
38 + 0 = 38
Identity Property of Addition
58 + 62 =
60 + 60 = 120
4,153 + 2,988 =
7,141
What is mental math?
Math you do in your head.
What does = mean?
"equals" or "the same as"
6,347 + 345 = 345 + 6,347
Commutative Property of Addition
99 + 25 =
100 + 30 = 130
92,425 + 31,675 =
124,100
What are some mental math strategies we learned?
Break apart, counting on, compensation.
What are the four operations in math?
(35 + 72) + 98 = 35 + (72 + 98)
Associative Property of Addition
4,613 + 3,211 =
5,000 + 3,000 = 8,000
41,542 - 32,411 =
9,131
When I use the break apart strategy, how do you break the numbers apart?
You break them up by place value.
Why do you round numbers?
to make them easier to use.
Use the Commutative Property to write this equation a different way:
36 + 98 = 134
98 + 36 = 134
32,788 + 68,222 =
33,000 + 68,000 = 101,000
735,184 - 255,863 =
479,321
What is compensation?
When you change the numbers to make the problem easier, but then have to "fix" your answer.
Why do you estimate?
You estimate to make sure your answer is reasonable?
Give an example of the Identity Property of Addition. Then, explain it.
Any number plus zero stays the same.
Is this estimate correct?
212,999 + 32,333 =
220,000 + 32,000 =
No, you would round 212,999 to either 210,000 or 213,000.
The Nile River is 7,088 kilometers long. The Amazon River is 6,575 kilometers long. How much longer is the Nile?
513 kilometers
Norah had to add 99 + 166. She did this:
"Instead of 99, I will use 100.
100+ 166 = 266."
What did she forget to do? What mental math strategy is this?
She forgot to subtract the 1 that she added to 99. The real answer is 265. She was trying to use compensation.
Why should you set up your scrap paper neatly?
You can make mistakes if you try to do the math in your head or set it up sloppily.