**Elementary School Number Sense Lesson 15: Adding and Subtracting Whole Numbers**

Over a year ago, we covered

**AddWhole**and

**SubWhole**. Now we'll combine the two ideas. These problems have shown up

**6 times**this year, with a median placement at

**question # 67**.

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**Number Dojo Level: 28**

These look pretty straightforward, but they can take too much time if you’re not careful.

**How to Solve:**

- Look for a pattern in the numbers.
- If possible, add and subtract in pairs.
- Add or subtract whatever is left over.

**Example 1: 23 + 23 + 23 – 17 – 17 – 17 = ___**

- Pair each 23 with a -17, and the difference is
**6** - There are 3 pairs, so 3 x 6 =
**18**

**Example 2: 15 – 23 + 17 – 21 = ___**

- Break this into pairs: (15 – 23) + (17 – 21)
- We’re left with -8 + -4, which is
**-12**

**Example 3: 11 + 14 + 17 – 20 = ___**

- Notice that the first 3 numbers form an arithmetic sequence, with the terms 3 apart. That makes their sum 3 x 14 =
**42** - We’re left with 42 – 20, which is
**22** - Another way to solve this is to break it into pairs: (11 + 14) + (17 – 20), which is 25 + -3, which is
**22**

**Example 4: 63 – 57 + 43 – 37 + 23 – 17 = ___**

- Break this into pairs: (63 – 57) + (43 – 37) + (23 – 17).
- Each difference is 6. 3 x 6 =
**18**

**Example 5: 40 – 36 + 32 – 28 + 24 = ___**

- Break this into pairs: (40 – 36) + (32 – 28) + 24
- Each difference is 4. 4 + 4 + 24 =
**32**

**Example 6: -5 + (-5) – (-5) + 5 – 5 = ___**

- Handle these in pairs like this: (-5 + -5) – (-5) + (5 – 5)
- -10 + 5 + 0 =
**-5**

**Here's a free worksheet to help you practice AddSubWhole:**

addsubwhole.pdf |

**Up Next for Elementary School: Parallelogram**