ACT Math : How to find the perimeter of a pentagon

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #24 : Plane Geometry

One side of a regular pentagon is . Find the perimeter of the pentagon. 

Possible Answers:

Correct answer:


In a regular pentagon, all of the sides are the same length.

The perimeter can then be found by summing all  sides or multiplying  by

Example Question #31 : Plane Geometry



What is the perimeter of the regular pentagon pictured above?

Possible Answers:

The answer cannot be determined.

Correct answer:


The key word in this question is "regular." Since the pentagon is regular, all of its sides are equal. This means that it, in fact, looks like:


The perimeter for this is simply  or .

Example Question #32 : Plane Geometry

A regular pentagon has a side length of . Find its perimeter.

Possible Answers:

Correct answer:


Because we're told the pentagon is a regular polygon, this means that all of its sides are the same length. That is, the side lengths are congruent.

In order to solve for the perimeter, which is the sum of all sides, we can use a multiplication shortcut of:

, where  is perimeter,  is length of the sides, and  is the number of sides of the polygon. 

Using the information given in the problem, the values can be substituted in.

Note that this math is the same as adding  five times:

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