The area on the wall covered by a rectangle is 320 square inches. the length of the poster is 1.25 times longer than the width of the poster. what are the dimensions of the poster?

To answer this question you will think of the length and the width as the following:
Length- 1.25w
Width-w

Using this you can then substitute in the information in your formula for finding the area of a rectangle.

A = lw
320 = 1.25w(w)
320 = 1.25 w^2; divide both sides by 1.25

256 = w^2; find the square root of both sides

w = 16 in

l = 1.25 x 16
l = 20 inches

The dimensions are a width of 16 inches and a length of 20 inches.