How does it work?

Option 1: Just fill in the form with your homework question, and someone will respond shortly with an answer.

Option 2: Take a photo (or link) of your question, and email or text it to us.

Like us?

Perimeter of a Rectangle, Two Unknowns

Q: The perimeter of a rectangle is 74 inches. If the width is doubled and the length is halved, the new rectangle will have a perimeter is 76 inches. What are the dimensions?

A: You have two unknowns, l=length and w=width, so you need two equations.

Recall that perimeter of a rectangle is P = 2l + 2w

Eqn 1: 74 = 2w + 2l
Eqn 2: 76 = 2(2w) + 2l/2
76 = 4w +l
Rearrange Eqn. 2, isolating for l:


Insert this expression for l into Eqn 1:

74 = 2w + 2(76-4w)
74 = 2w + 152 -8w
6w = 78

The length can be found from either Eqn 1 or 2:
l = 76-4w
l = 76-4(13)

So the width is 13 inches and the length is 24 inches.