The document discusses calculating decimal numbers by adding and subtracting. It provides examples of lining up decimals, adding or subtracting like normal, and using the commutative and associative properties of addition to evaluate expressions by changing the grouping or order of numbers. Students are asked to find the total cost of various school supplies by adding decimal prices.

1. How might we represent 3 + 6.5 + 7 + 11.5 in a different way?

2. Learning Target:Students will learn how to calculate decimal numbers by adding and subtracting. Students will learn the communicative and associative properties of addition.

3. BIG IDEAS:MUST LINE UP YOUR DECIMALSADD ZEROS WHERE NECESSARYBRING DECIMAL STRAIGHT DOWN ADD OR SUBTRACT LIKE NORMAL

4. Find the sum or difference.3.286 + 4.5115 – 2.08

5. Answers: 3.286+4.510 7.79615.00- 2.0812.92

6. Evaluate the expression when x = 5.82 and y = 9.1.4.7 + xy – x

7. Answers: 4.70+ 5.82 10.52 9.10- 5.82 3.28

8. Properties of Addition:Commutative Property – You can add numbers in any order.2 + 4 = 4 + 2a + b = b + aAssociative Property – The value of a sum does not depend on how the numbers are grouped.(2 + 4) + 5 = 2 + (4 + 5)(a + b) + c = a + (b + c)

9. Tell which property is being illustrated. Then use mental math to evaluate the expression in red.(6.4 + 4.8) + 5.2 = 6.4 + (4.8 + 5.2) 9.3 + 2.9 = 2.9 + 9.3

10. Answers:(6.4 + 4.8) + 5.2 = 6.4 + (4.8 + 5.2)Associative Property(the groupings changed)16.49.3 + 2.9 = 2.9 + 9.3Commutative Property(the order changed)12.2

11. 1st person: Find the total cost for a pair of headphones that costs $19.75, two CDs that cost $11.50 each and a pack of batteries that costs $4.25.2nd person: Find the total cost for two notebooks that cost $1.45 each, two pads that cost $0.55 each and one box of pencils that cost $2.75.Share your answer with the other person

12. Answers:Total cost of the CDs, head phones and batteries is $47.00.Total cost for the box of pencils, 2 pads of paper and 2 notebooks is $6.75.

13. Can you calculate decimal numbers by adding and subtracting?