Dear Parents,

Let’s look at *Adding and Subtracting within 100*
In Second Grade we are now working on **fluently** adding and subtracting within 100 using strategies based on place value and the relationship between addition and subtraction. We are using many tools to help us.
Our learning targets are:
I can add and subtract numbers within 100 with ease by applying strategies:
- decomposing numbers into tens and ones
- using
*commutative* and *associative* properties
- using mental strategies
Don’t forget to ask: |

*How do you know you’re right?*

For this week’s problems you will need to use *straws *and a *hundred chart*. (See below for an easier way of putting those **straws** together into bundles!)

For Friday’s activity, **Addition Battle***, *you will need a **deck of cards **(buy at a **stationary shop** – – **papelería** – – or school supply and toy store such as **Abacus**

http://abacus.coop/ca/la-cooperativa/botigues-abacus/ .

Type in your **zip code** – – **código postal** – – to find nearest shop.).

The Second Grade Team

**Decomposing numbers**: breaking apart numbers so that they can be used more easily in subtraction problems. For example, 32 could be made and then drawn as 3 groups of ten and 2 ones, or as 2 groups of ten and 12 ones.

**Commutative property**: you can change numbers around and still get the same answer when you add or multiply.

Examples:

You can change the order when you add: 3 + 6 = 6 + 3

You can change the order when you multiply: 2 × 4 = 4 × 2

**Associative property**: it doesn’t matter how you group the numbers when you add or multiply.

(In other words it doesn’t matter which you calculate first.)

Example addition: (6 + 3) + 4 = 6 + (3 + 4)

Because 9 + 4 = 6 + 7 = 13

Example multiplication: (2 × 4) × 3 = 2 × (4 × 3)

8 × 3 = 2 × 12 = 24

**Suggestions for making sets of straws **(without buying industrial quantities of them)**:**

– Buy two or three bags of straws (cheap is fine!)

– Buy or gather together some rubber bands

– **Take ten straws, **put** rubber band around them at equidistant points (at middle, at bottom, at top) **and then** cut the set of ten straws into thirds. **Now you have three groups of ten**.**

– Repeat with more groups of ten straws.

– To make a** group of 100, take ten groups of ten, **and** tie them together with yarn or string.**

– Ones can be made out of straws cut into thirds.

– **If you prefer larger sized manipulatives, just cut straws in half, and not into thirds.**

**Suggestions for making sets of straws****:**

– **Buy two bags of straws (cheap is fine!)**

– **Buy or gather together some rubber bands**

– **Take ten straws, put rubber band around them at equidistant points (at middle, at bottom, at top) and then cut the set of ten straws into thirds. Now you have three groups of ten.**

– **Repeat with more groups of ten straws.**

– **To make a group of 100, take ten groups of ten, and tie them together with yarn or string.**

– **Ones can be made out of straws cut into thirds.**

– **If you prefer larger sized manipulatives, just cut straws in half, and not into thirds.**

**Suggestions for making sets of straws****: **

– Buy two bags of straws (cheap is fine!)

– Buy or gather together some rubber bands

– Take **ten straws**, **put rubber band around them at equidistant points (at middle, at bottom, at top)** and then **cut the set of ten straws into thirds**. Now you have three groups of ten.

– Repeat with more groups of ten straws.

– To make a **group of 100**, take **ten groups of ten**, and **tie them together** with yarn or string.

– Ones can be made out of straws cut into thirds.

– If you prefer **larger sized manipulatives**, just **cut straws in half**, and not into thirds.