The answer to an addition problem.
The answer to a subtraction problem.
Sum and Difference
5.58 - 2.43 = ?
3.15
3.52 + 7.14 = ?
10.66
Estimate the sum of 12.39 and 8.96 by rounding each number to the nearest whole number.
21
At the grocery story, Lily bought a box of cereal for $3.78 and a gallon of milk for $4.50. How much money did she spend in all?
$8.28
The property that lets you add two decimals in any order.
Commutative Property
11.26 - 7.8 = ?
3.46
13.21 + 29.7 =
42.91
Estimate the difference between 27.9 and 16.93 by rounding each number to the nearest whole number.
11
Eric found a pair of sneakers for $85.60. He has a coupon for $7.50 off a pair of sneakers. How much money will Eric pay for the sneakers after his coupon?
$78.10
Numbers that are easy to add, subtract, multiply, and divide mentally.
Compatible Numbers
$56.98 - $28.99 = ?
$27.99
$3.90 + $12.99 + $41.20 = ?
$58.09
Estimate the sum of 29.49 and 13.82 by rounding each number to the nearest tenth.
43.3
Henry has three toy cars with different lengths. The red car is 6.79 cm, the blue is 3.2 cm, and the yellow is 12.32 cm.
1. What is the combined lengths of the cars?
2. How much longer is the yellow car than the blue car?
1. 22.31 cm
2. 9.12 cm longer
The properties that lets you change the groupings of the addends.
Associative Property
What decimal makes this equation true?
4.67 + ____ = 12.37
7.70
15.9 + 26.29 + 43 = ?
85.19
Estimate the difference of 43.72 and 38.26 by rounding each number to the nearest tenth.
5.4
At the book fair, Natalie spent $12.78 on a book and $8.99 on highlighters.
1. What is the total amount she spent at the book fair?
2. If she paid with a $50 bill, how much change would she get?
1. $21.77
2. $28.23
A mental math strategy that involves changing the number in an equation to make it easier to solve, while still keeping the equation balanced.
Compensation
What decimal makes this statement true?
86.39 + ______ = 198.23
111.84
$100 + $65.90 + $203.97 + $43
$412.87
21.3 cm
A bathroom is 40.36 feet long and 29.27 feet wide.
1. Round the width and the length to the nearest whole number. Then estimate the perimeter of the bathroom.
2. Round the width and the length to the nearest tenth. Then estimate the perimeter of the bathroom.
3. Find the actual perimeter. Which estimate is closer to the actual perimeter
1. 138 feet
2. 139.4 feet
3. 139.26; Rounding to the tenths