Vocabulary
A number close to an exact value.
Estimate
364+16=
380
35 to the nearest 10
40
572+632=
1,200
Students have borrowed 632 fiction books and 492 non-fiction books from the school library. Is it reasonable to say the students borrowed about 1,100 books? Explain.
Yes, the number of books students borrowed was 1,124. If I round to the nearest hundred, I get 1,100.
Ordering or grouping numbers so they are easier to add in your head.
Mental Math
936+49=
985
161 to the nearest 10
160
977+134=
1,100
Students from Sydney Elementary School have entered a National Poetry contest. There are 19 second graders, 23 third graders, and 9 fourth graders who have entered. Are there at least 50 students entered in the contest? Explain.
Yes, because 51 students entered the contest. I know 51 is greater than 50.
Symbols that are used to group numbers. They show how to group operations in a number sentence.
Parentheses
469+641=
1,110
345 to the nearest hundred
300
1,769+1,270=
3,000
The head of Gracie's favorite dinosaur is 14 feet long, the body is 26 feet long, and the tail is 19 feet long. Is it reasonable to say the entire dinosaur is 60 feet long? Explain.
Yes, the sum of the addends is 59 feet. If I round 59 to the nearest 10, I get 60 feet.
The property states that the grouping of addends does not change the sum.
(6+4)+2=(6+2)+4
The Associative Property
6,921+2,159=
9,080
2,794 to the nearest hundred
2,800
1,921+344=
2,265
Mr. Messinger has 364 toy cars and 609 toy trucks. Is it reasonable to say that Mr. Messinger has about 800 toys altogether? Explain.
No, Mr. Messinger has a total of 973 toys. 973 toys are closer to 1,000 than 800.
If you add zero to a number, the sum is the same as the given number.
3+0=3
Identity Property
9,798+3,311=
13,109
6,517 to the nearest thousand
7,000
1,677+8,931=
11,000
Why do we check to make sure our answer is reasonable?
We check for reasonability to make sure that our answer is correct and makes sense.