Given the perimeter of a rectangle and either the length or width, find the unknown measurement using the appropriate formula.

The perimeter is 76 cm and the length is 20 cm.

What is the width of the rectangle? Show all your work

Hi there,

A rectangle has got 2 lengths, and 2 widths, so we have got the formula:

P = 2·L + 2·l, where P - perimeter, L - length, and l - width.

P - - 2·L = 2·l, if we divide everything by 2, we have

P/2 - - L = l, so l = P/2 - - L = 76/2 - - 20 = 38 - - 20 = 18 cm, so l = 18 cm.

Was it difficult?

Green eyes.

The fromula of a perimeter of rectangle:

P = 2 (l + w)

We have P = 76 cm and l = 20 cm.

Substitute:

2 (20 + w) = 76 use distrubutive property

(2) (20) + (2) (w) = 76

40 + 2w = 76 subtract 40 from both sides

2w = 36 divide both sides by 2

w = 18

Answer: the width = 18 cm