Bunuel

A flat rectangular picture, represented by the unshaded region in the figure above, is mounted in a flat rectangular frame, represented by the shaded region. The frame is 1 inch wide on all sides. For what value of x, in inches, is the area of the frame equal to the area of the picture?
A. 4
B. 5
C. 6
D. 7
E. 8
We'll show two approaches.
The first relies on using the figure without any calculations.
This is an Alternative approach.
The top and bottom part of the frame each have width x and height 1 so their area is x.
The left and right part of the frame (without the corners) each have width 1 and height x so their area is x.
So the area of the frame is 4x.
Since the picture has height x, for it to have 4x area it must have a width of 4.
Then x = 4 + 2 = 6.
(C) is our answer.
The second is an equation driven, a Precise approach.
The area of the frame is the area of the large rectangle (frame+picture) minus that of the picture.
The area of the picture is the product of its height and width.
Since the frame has width is 1 inch on all sides, the large rectangle has area x*(x+2) = x^2 +2x
The picture has height x and width x - 2 so its area is x*(x-2) = x^2 - 2x.
Then the frame has area x^2 + 2x - (x^2 - 2x) = 4x
So, the two are equal when x^2 - 2x = 4x --> x^2 - 6x = 0 --> x(x - 6) = 0 and x = 6.
(C) is our answer.