1. Addition and subtraction number stories
Grade 5 lesson 2.4
Addition and subtraction number stories
Objective: to review the use of mathematical models to solve number stories

2. Math Message
Niko has $ Does he have enough money to buy 3 fancy pencils for $1.98 each and an eraser for $1.73?
What is the total cost of the 3 pencils and the eraser?
How did you find this information out? Write it in your ISN.

3. Number Sentences (write these in your ISN)
A true number sentence is a sentence in which the relation symbols and operation symbols combine to create a sentence where both sides of the sentence are equal to each other.
A false number sentence has sides that are not equal to each other.
A number sentence that contains a variable is called an OPEN number sentence.
Open number sentences are neither true or false. (they become true or false when we replace the variable with a number.
4 + 5 = 9
4 + 5 = 31
4 + 5 = x

4. Relation & operation symbols (write these in your isn)
Relation Symbols
< means is less than
> means is greater than
= means is equal to
Operation Symbols
+ means plus
- means minus
X or * means times
/ or ÷ means divided by
Number sentences MUST have a relation symbol.
Number sentences MUST also have an operation symbol.

5. What makes a good problem solver?
A good problem solver is someone who has learned how to organize information to find a solution when he or she is not sure how to get the correct answer.
Learning many different ways to do many different types of problems gives you the ability to organize information in many different ways.
Find page 41 – Situation Diagrams
Open your Student Reference Book to pages
Read the four steps of the guide and determine the type of situation in the problem. Is it – parts and total? Change to more? Change to less? Or is it a comparison problem?

6. Find math masters page 42
In pairs or groups of 3, complete lesson 2.4 Math masters page 42, Using Open number sentences.
Remember, an Open Number Sentence uses a VARIABLE. You MUST have a letter in place of an unknown number in your sentences.
What letter do you choose? You CAN choose ANY letter. However, most people choose a letter that represents what they are trying to find out. For example, if I wanted to know how many tea bags fell into the Boston Harbor, I might use the letter t. (Always use a lowercase letter for now.)

7. Further practice Complete student workbook pages 37 and 38.
You may need to use page If you need a computational grid, feel free to get yourself one.
(a computational grid is grid paper!) We have it in whiteboard form as well.

8. Game
Name that Number (student reference book page 325)

9. Homework – Enrichment – Extra Practice
Page 43 Open Sentences and Number Stories is homework for this lesson.
Please complete page 44 if you would like additional practice. – Using situation diagrams.
Enrichment for this lesson is page 45 – Writing open number sentences.