gmatophobia
gmatophobia
PS Question 1 - Nov 21
A square wooden plaque has a square brass inlay in the center, leaving a wooden strip of uniform width around the brass square. If the ratio of the brass area to the wooden area is 25 to 39, which of the following could be the width, in inches, of the wooden strip?
I. 1
II. 3
III. 4
(A) I only
(B) II only
(C) I and II only
(D) I and III only
(E) I, II , and III
Solution:
Let a side of the brass inlay in the center be x. Let’s analyze each statement:
I. 1
If the width of the uniform strip is 1, then a side of the entire wooden plaque is x + 2. Thus, the ratio of the area of the brass inlay to the wooden area is x^2 / [(x + 2)^2 - x^2]. Since we are told that this ratio is 25/39, let’s create the following equation:
x^2 / [(x + 2)^2 - x^2] = 25/39
39x^2 = 25[x^2 + 4x + 4 - x^2]
39x^2 = 100x + 100
39x^2 - 100x - 100 = 0
(3x - 10)(13x + 10) = 0
x = 10/3 or x = -10/13
Since there is no restriction on x (such as the side of the wooden plaque should be an integer etc.), it is possible that a side of the plaque is 10/3. We see that the width of the wooden strip can be 1.
II. 3
If the width of the uniform strip is 3, then a side of the wooden plaque is x + 6. Thus, the ratio of the area of the brass inlay to the wooden area is x^2 / [(x + 6)^2 - x^2]. Since we are told that this ratio is 25/39, let’s create the following equation:
x^2 / [(x + 6)^2 - x^2] = 25/39
39x^2 = 25[x^2 + 12x + 36 - x^2]
39x^2 = 300x + 900
39x^2 - 300x - 900 = 0
13x^2 - 100x - 300 = 0
(x - 10)(13x + 30) = 0
x = 10 or x = -30/13
We see that a side of the wooden plaque can be 10, and the width of the wooden strip can be 3.
III. 4
If the width of the uniform strip is 4, then a side of the wooden plaque is x + 8. Thus, the ratio of the area of the brass inlay to the wooden area is x^2 / [(x + 8)^2 - x^2]. Since we are told that this ratio is 25/39, let’s create the following equation:
x^2/[(x + 8)^2 - x^2] = 25/39
39x^2 = 25[x^2 + 16x + 64 - x^2]
39x^2 = 400x + 1,600
39x^2 - 400x - 1,600 = 0
(3x - 40)(13x + 40) = 0
x = 40/3 or x = -40/13
We see that a side of the wooden plaque can be 40/3 and the width of the wooden strip can be 4.
Answer: E