1. Estimating Sums

2. Estimation and Rounding
How can we use what we know about rounding to estimate?
Estimating sums is best done by rounding the addends, then adding?

3. Estimation and Rounding
3,456
+ 687
Step 1- Round the addends to the largest place value both numbers have in common.
What is the largest place value in common?

4. Estimation and Rounding
3,456
+ 687
The hundreds place is the largest place value the two addends share in common.

5. Estimation and Rounding
3,456
687
Round both addends to the nearest hundred.
Use the poem to help.
Find your number.

6. Estimation and Rounding
3,456
687
Look right next door.

7. Estimation and Rounding
3,456
687
4 or less, just ignore.
Both the 5 and 8 are greater than 4, so move to the next line of the poem.

8. Estimation and Rounding
3,456
687
5 or more, add one more.
Both the 5 and 8 are 5 or greater, so add 1 to the numbers in the hundreds place. (4 and 6)

9. Estimation and Rounding
+ 1
+ 1
3,456
687
5 or more, add one more.
Both the 5 and 8 are 5 or greater, so add 1 to the numbers in the hundreds place. (4 and 6)

10. Estimation and Rounding
+ 1
+ 1
3,456
687 3,
Any number to the left remains unchanged. The 3 in 3,456 is unchanged.

11. Estimation and Rounding
+ 1
+ 1
3,456
687 7 3, 5
Add the 1 to the place value you are rounding.

12. Estimation and Rounding
+ 1
+ 1
3,456
687 3, 5 7
All of the remaining numbers to the right become zeros.

13. Estimation and Rounding
3,500
+ 700
4,200
Finally, add the rounded numbers.

14. Estimation and Rounding
3,456
+ 687
4,200
The estimate is about 4,200.

15. 5-2 Estimating Sums and Differences
Example
Susan is worried that she has spent too much money. She has $256 in her checking account and has written checks for $92.69, $126.58, $9.58, and $12.39.
Determine if Susan has spent too much money.

16. 5-2 Estimating Sums and Differences
Example
Susan is worried that she has spent too much money. She has $256 in her checking account and has written checks for $92.69, $126.58, $9.58, and $12.39.
Determine if Susan has spent too much money.
Round each check to the nearest dollar amount.

17. 5-2 Estimating Sums and Differences
Example
Susan is worried that she has spent too much money. She has $256 in her checking account and has written checks for $92.69, $126.58, $9.58, and $12.39.
Determine if Susan has spent too much money.
Round each check to the nearest dollar amount. ®

18. 5-2 Estimating Sums and Differences
Example
Susan is worried that she has spent too much money. She has $256 in her checking account and has written checks for $92.69, $126.58, $9.58, and $12.39.
Determine if Susan has spent too much money.
Round each check to the nearest dollar amount. ®
® 126

19. 5-2 Estimating Sums and Differences
Example
Susan is worried that she has spent too much money. She has $256 in her checking account and has written checks for $92.69, $126.58, $9.58, and $12.39.
Determine if Susan has spent too much money.
Round each check to the nearest dollar amount. ®
® 126 ®

20. 5-2 Estimating Sums and Differences
Example
Susan is worried that she has spent too much money. She has $256 in her checking account and has written checks for $92.69, $126.58, $9.58, and $12.39.
Determine if Susan has spent too much money.
Round each check to the nearest dollar amount. ®
® 126 ®
® +12

21. 5-2 Estimating Sums and Differences
Example
Susan is worried that she has spent too much money. She has $256 in her checking account and has written checks for $92.69, $126.58, $9.58, and $12.39.
Determine if Susan has spent too much money.
Round each check to the nearest dollar amount. ®
® 126 ®
® +12
241

22. 5-2 Estimating Sums and Differences
Example
Susan is worried that she has spent too much money. She has $256 in her checking account and has written checks for $92.69, $126.58, $9.58, and $12.39.
Determine if Susan has spent too much money.
Round each check to the nearest dollar amount. ®
® 126 ®
® +12
241
Since 241 < 256, Susan has enough money in her account.