The length of a rectangle is 5 centimeters less than twice it's width. The perimeter of the rectangle is 80 cm. What are the dimensions of the rectangle

Question

I need a answer to this problem. Also, can you show me how you got the answer so that I can explain it to my student.

Answer 1

perimeter= sum of all 4 sides.  rectangle has two pairs of equal sides.  So, length=(2w-5) and width = w.
So, 80=w+w+(2w-5) + (2w-5)

So 80=2w+4w-10

80=6w-10

add 10 to both sides

90=6w

divide both sides by 6

15=w
So if w=15, then plug in 15 for w into equation for length: 2w-5 and you will get 25.

25 x 15

Answer 2

Let w = the width

Let 2w-5 = the length

P = 2l + 2w

80 = 2(2w-5) + 2(w)

80 = 4w - 10 + 2w

90 = 6w

w = 15 cm

length = 2(15) - 5 = 30 - 5

length = 25 cm