Mental Math
Estimate Sums and Differences
Add and Subtract Decimals
Add Decimals
Subtract Decimals
Model with Math
100

Use mental math to solve: 5.7 + 4.3 + 6

sample answers:

0.3 + 0.7 = 1.0, then 1 + 5 + 4 + 6 = 16

or....5.7 + 4.3 = 10, 10 + 6 = 16


100

Estimate the sum:

3.8 + 4.1 + 3.3

3.8 rounds up to 4

4.1 rounds down to 4

3.3 rounds down to 3

4 + 4 + 3 = 11

100

Write an expression that is represented by the model below:

1.45 - 0.31

100

Find the sum

1.03 + 0.36

1.39

100

Find the difference.

13.9 - 3.8

10.1

100

Ciarra saved $12 in March, $15.75 in April, and $10.90 in May. Then she bought a shirt for $23.60. How much money does Ciarra  have left? 

$12 + 15.75 + 10.90 = 38.65

38.65 - 23.60 = 15.05

Ciarra  has $15.05 left.

200

Use mental math to solve: 275 + 180 + 120

180 + 120 = 300, then 300 + 275 = 575

200

Estimate the difference:

788.9 - 572

788.9 rounds up to 800

572 rounds up to 600

800 - 600 = 200

200

Each set of place-value blocks below represents a decimal. 

Write and solve the equation represented by the place-value blocks below.

0.32 + 0.75 = 1.07

200

Find the sum.

45.08 + 2.01

47.09

200

Find the difference.

8.04 - 0.3

7.74

200

Haiden has $15. He buys a ticket to a movie for $9.50 and a smoothie for $2.85. How much money does he have left?

15.00 - 9.50 - 2.85 = $2.65.

Haiden has $2.65 left.

300

Laila bought three books that cost $3.95, $4.99, and $6.05. How much did she spend in all?


She spent $ 14.99 in all.

300

Three rock samples have masses of 74.05 grams, 9.72 grams, and 45.49 grams. Anela estimates the total mass of the samples by rounding each mass to the nearest whole number.

What are the numbers when rounded to the nearest whole number?

74.05 = 74

9.72 = 10

45.49 = 45

300

Emmanuel collected rocks that has a mass of 54.14 grams. Javon started to collect rocks and so far has 8.98 grams. Serenity decided to join and collected 7.39 grams of rocks. What is the total grams of their collection? What is the difference between the heaviest mass and the lightest?

Total= 70.51 grams

Difference = 46.75 grams

300

Find the sum.

7.2 + 3.96 + 8.8

19.96


300

Find the difference.

34.49 - 12.61

21.88


300

For her birthday, Diana received $20 from her aunt, $15 from her grandmother, and $32 from her cousins. She bought an e-book for $10.85. How much birthday money does Kyrah have left?

20 + 15 + 32 = $67

67 - 10.85 = $56.15

Diana has $56.15 left.

400

Describe and give an example of the commutative property.

The Commutative Property lets you add two decimals in any order.

ex: $11.45 +$3.39 = $3.39 + $11.45

400

Edward buys a game for $7.89 and some batteries for $5.49. He pays with a $20 bill. What is the best estimate of how much change he should get?

7.89 = 8; 5.49 = 5

5 + 8 = 13; 20 - 13 = 7

The best estimate is $7.00 in change.

400

Emory gave Amoya a rug for her birthday. The rug is 14.72 ft wide and 24. 05 ft long. About how big is the perimeter of the rug to the nearest whole number?

+ 400 points: Is the estimate bigger or smaller than the actual perimeter? How much bigger or smaller?

about 78 ft long

The estimate is .46 ft bigger.

400

Annabella earned $16 babysitting and $17.50 mowing a lawn. She paid $8.50 for a movie and bought a small popcorn for $1.95. Write an expression to show how much money she has left, and solve.

16 + 17.50 - 8.50 - 1.95 = $ 23.05

400

Ruben bought a book for $35.60 and a set of pens for $12.78. How much did he spend in all? If he paid with three $20 bills , How much change did he get?

$48.38 = total amount he spent

$11.62 = his change from $60.00

400

Conrad paid $52.26 for a pair of shoes. Michelle paid $3.89 more for a pair of shoes than Conradpaid for his. 

How much did Michelle pay for her shoes? Use the bar diagram to help you.

Michelle paid $56.15 for her shoes.

500

Describe and give an example of the Associative Property.

The Associative Property lets you change the grouping of addends.

ex: ($11.45 +$3.39)+$9.55 =$11.45 +($3.39 +$9.55)

500

The cost of one DVD is $16.98, and the cost of another DVD is $9.29. I'sere estimated the cost of the two DVDs to be about $27. Is his estimate higher or lower than the actual cost? Explain.

His estimate is lower because he rounded 16.98 up to 17 and 9.29 up to 10. The actual cost is $26.27.

500

Jayla put 3 shelves in her room.The top is 2.55 feet long. The middle is 2.25 feet long, and the bottom shelf is 3.88 feet long. What is the combined length of the 3 bookshelves? How much longer is the bottom shelf than the top shelf?

8.68 feet long = 3 shelves

The bottom shelf is 1.33 feet longer.

500

Choose all expressions that are equal to 12.9.

500

Janiyah bought 8.6 lbs. of strawberries, Kaitlyn bought 40.44 lbs of strawberries, Tahj bought 23.5 pounds of strawberries, and Riley bought 34.5 lbs. of strawberries. What is the difference between the amounts Janiyah bought from the amount of each of the other people bought?

Kaitlyn bought 31.84 lbs. more strawberries than Janiyah.

Tahj bought 14.9 lbs more strawberries than Janiyah.

Riley bought 25.9 more strawberries than Janiyah.


500

Wyh'iel has $15.50 and Jacob has $15.00. They want to buy Mrs. Maglantay a sweater that costs $15, a chocolate that costs $3.79, and a scarf that costs $14.79. 

Do they have enough money? Explain how you kmow and show your work.

They don't have enough money.

15+ 15.50=30.50

15 + 3.79 + 14.79 = 33.58

33.58 - 30.50 = $3.08

They need $3.08 more.