Question

The length of a rectangle is twice the width. Find the width if the perimeter is 60 centimeters. Define a variable, write an equation, and solve the problem.

Answer 1

Call the length $l$ and the width $w$. We know that:
1. "The length of a rectangle is twice the width." i.e.: $l=2w$
2. "the perimeter is 60 centimeters." i.e.: $P=60$

Using the perimeter formula $P=wl+2w$ we have:
$60=2l+2w$
$60=2l+l$
Thus:
$l=20$
and:
$w=\frac{l}{2}$
$w=10$

The rectangle is 20cm long by 10cm wide. 

To check:
$P=2l+2w$
$60=2(20)+2(10)$
$60=40+20$
$60=60$  Checks true. 

Answer 2

width = w

length = 2w

perimeter = 2w + 2 l

perimeter = 2w +2(2w)

60 = 2w + 4w

60= 6w

60=6w

w = 60/6 = 10

length = 10x2 = 20

10+10+20+20 = 60