**Middle School Number Sense Lesson 17: Squaring Numbers Ending in 5**

This concept showed up a mere

**6 times**this year--usually at around

**question # 17**. Since it is the backbone of a few other concepts, I wanted to cover it even though other concepts are a little more common.

**Number Dojo Level: 53**

There are 2 easy steps to solving these problems:

- Write down the number
**25**(yes, seriously!).**Every one of these answers ends in a 25.** - Multiply the 10s digit by its upper neighbor (the next counting number--in other words, itself plus 1). Write this down in front. You are DONE.

**Example 1: 25 x 25**

- Write down
**25**. - Multiply the 10s digit by its upper neighbor. 2 x 3 =
**6**. Write this down in front. The answer is**625**.

**Example 2: 85 x 85**

- Write down
**25**. - 8 x 9 =
**72**; write this in front. The answer is**7225**.

**Example 3: 55 x 55**

- Write down 25.
- 5 x 6 = 30; write this in front. The answer is
**3025**.

**Example 4: 105 x 105**

- Write down
**25**. - This is (barely) trickier. Instead of considering just the 10s digit, look at everything in front of the 5. 10 x 11 =
**105**; write this in front. The answer is**11025**.

**Example 5: 7.5 x 7.5**

- Write down
**25**. - Don't let the decimals fool you. 7 x 8 =
**56**; write this in front. Remember to include 2 decimal places. The answer is**56****.25**.

**Here's a free worksheet to help you practice SquareEnd5:**

squareend5.pdf |

**Up Next for Middle School: Mult10s,U+10**