**Middle School Number Sense Lesson 93: Calculating with the Number of Sides of a Polygon**

This concept has shown up

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

**question # 45**.

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**Number Dojo Level: 136**

It may be helpful for you to review

**PolygonDiag**, which included a discussion about all the prefixes used to identify different polygons. The assumption made in each problem is that each side of the polygon has equal length. These are usually simple calculations, once you have determined how many sides the polygon has.

**Example 1: The perimeter of a regular octagon with an edge of 125 is ___**

- An octagon has
**8**sides. - To find the perimeter, multiply 8 by 125. The answer is
**1000**.

**Example 2: The perimeter of a regular pentagon with side length 8.6 cm is ___ cm**

- A pentagon has
**5**sides. - Multiply 5 x 8.6 to find the perimeter (use
**Double/Half**to simplify this). 5 x 8.6 = 10 x 4.3, which is**43**.

**Example 3: The perimeter of a dodecagon with side 9 is ___**

- A dodecagon has
**12**sides. - 9 x 12 =
**108**.

**Example 4: The perimeter of an undecagon with edge length 24 is ___**

- An undecagon has
**11**sides. - 11 x 24 (using
**Mult11**) =**264**.

**Example 5: If the perimeter of a regular hexagon is 78, then the length of each side is ___**

- A hexagon has
**6**sides. - 78 ÷ 6 =
**13**.

**Up Next for Middle School: BaseSub**