PROBLEM

SOLVING PLAN1. READ and UNDERSTAND the problem.

2. PLAN how to solve the problem.3. SOLVE it.4. LOOK BACK and CHECK to see if your

answer makes sense.

Do You Remember?

Adding and Subtracting Decimals

Lesson 1-5

The Basic Steps:

1. Line up the numbers by the decimal point.

2. Fill in missing places with zeroes.

3. Add or subtract.

Addition PropertiesCommutative Property of Addition: Numbers can be added in any order.

Example: 5+3=3+5

Associative Property of Addition: Numbers can be grouped in any way.

Example: (7+3) + 5 = 7 + (3+5)

Identity Property of Addition: The sum of any number and zero is that number.

Example: 18 + 0 = 18

Mental Math• Addition properties can be used to quickly

find sums.• Example: What is 52 + 12.4 + 48?• We can use an addition property to

quickly add this. • First, change the order: 52 + 48 + 12.4

________________ property.• Then, group the first two addends

together: (52 + 48) + 12.4________________ property

• 100 + 12.4 = 112.4

commutative

associative

Example: 28.9 + 13.31This can estimate to 30 + 13, which is 43. (Compatible numbers)

28.913.31+

0

42.21The answer is close to the estimate.

Subtracting

• The addition properties do not work for subtraction.

• Estimate and subtract to find what the answer is close to.

• Subtract to find the real answer.

Subtracting Across Zeroes• If you have several zeroes in a row, and you need to borrow, go to the first digit that is not zero, and borrow.• All middle zeroes

become 9’s.

• The final zero becomes 10.

Example: 15 – 9.372

159.372-

.0004 9 9 10

826.

0 1

5

Classwork:• Play Hotel Decimalfonia to

help you add and subtract decimals

• Practice Adding Decimals and Subtracting Decimals from AAA Math

• Complete Adding/Subtracting Decimals worksheet

Homework Timepg. 27-28, #2-40 evens, pg. 32, #2-14 evens

The above image is of Detroit, MI from

http://www.leadersinstituteteambuilding.com/locations/team-building-detroit