The length of a rectangle is twice its width. The perimeter is 42cm. Find the length of each side.

Answer 1

l=2w

2l+2w=42

4w+2w=42

6w=42

w=7

l=14

Answer 2

Let's write some equations to represent the situation. The length is twice the width, so L=2w. We know that perimeter is the length of the outside of the rectangle, or 2L+2w, which sums to 42 cm. We have:

L=2w

2L+2w=42.

We can't solve one equation with two variables, so use 2w in place of L in the perimeter equation.

2(2w)+2w=42.

Multiply to get:

4w+2w=42. Adding the w's: 6w=42.

Divide both sides by 6 to get w=7.

The question asks for the length of each side, so we need the width and the length of the rectangle. Since L=2w, L=2(7)=14cm.

Two sides are 14cm, and two are 7cm.

I hope this helps! Geometry rocks!

Liz Z.