GOZUNTA
Try it now
All courses Math Foundations · MF.GM.2 49 of 60
Find and interpret perimeter and circumference in numeric and contextual problems.

Add the side lengths for perimeter

Problem
A rectangle has side lengths \(8~\text{cm}\) and \(5~\text{cm}\). What is its perimeter?
Your answer
Show answer choicesHide answer choices Work through the mathematics first, then compare your reasoning.Select the answer that matches your work.
With a free account

Share practice with a session code.

Every learning session has a code, making it easy to share the same included practice with someone else.

Create a free account
With paid access

Revisit a weak spot without repeating one problem.

Use additional variants to practice the same idea again while still having to do the mathematics.

Compare plans

Hint

Start by listing every outside side of the rectangle once. A rectangle has two 8 cm sides and two 5 cm sides.

Perimeter means the total distance around the outside of the shape, so add all four side lengths, not 8 × 5.

Solution walkthrough

01

Use the rectangle perimeter structure

\[P=2l+2w\]

A rectangle has two sides of length l and two sides of width w.

02

Source the dimensions

\[l=8~\text{cm};~w=5~\text{cm}\]

The prompt gives side lengths eight centimeters and five centimeters.

03

Substitute and calculate

\[P=2(8)+2(5)=16+10=26~\text{cm}\]

Add the lengths of all four sides.

04

Check by direct addition

\[8+5+8+5=26~\text{cm}\]

Walking once around the rectangle confirms the same total.

05

Report the perimeter

\[26~\text{cm}\]

The outside distance around the rectangle is twenty-six centimeters.

+

Another way

  1. Add one length and one width, 8+5=13, then double to get 26.

!

Common mistake

Do not multiply 8 by 5; that finds area, not the distance around the rectangle.

Solution walkthrough video